Fleiss’ Kappa

Introduction

Cohen’s Kappa is a measure of the agreement between two raters, where agreement due to chance is factored out. We now extend Cohen’s kappa to the case where the number of raters can be more than two. This extension is called Fleiss’ kappa. As for Cohen’s kappa, no weightings are used and the categories are considered to be unordered.

Formulas

Let n = the number of subjects, k = the number of evaluation categories, and m = the number of judges for each subject. E.g. for Example 1 of Cohen’s Kappa, n = 50, k = 3 and m = 2. While for Cohen’s kappa both judges evaluate every subject, in the case of Fleiss’ kappa, there may be many more than m judges, and not every judge needs to evaluate each subject; what is important is that each subject is evaluated m times.

For every subject i = 1, 2, …, n and evaluation categories j = 1, 2, …, k, let xij = the number of judges that assign category j to subject i. Thus

image7092

The proportion of pairs of judges that agree in their evaluation of subject i is given by

image7093

The mean of the pi is therefore

image7094

We use the following measure for the error term

image7095where

image7096

Fleiss’ Kappa and Standard Error

Definition 1: Fleiss’ Kappa is defined to be

image7088

We can also define kappa for the jth category by

The standard error for κj is given by the formula

The standard error for κ is given by the formula

image101c

There is an alternative calculation of the standard error provided in Fleiss’ original paper, namely the square root of the following:

image102c

The test statistics zj = κj/s.e.(κj) and z = κ/s.e. are generally approximated by a standard normal distribution. This allows us to calculate a p-value and confidence intervals. E.g. the 1 – α confidence interval for kappa is therefore approximated as

κ ± NORM.S.INV(1 – α/2) * s.e.

Example

Example 1: Six psychologists (judges) evaluate 12 patients as to whether they are psychotic, borderline, bipolar, or none of these. The ratings are summarized in range A3:E15 of Figure 1. Determine the overall agreement between the psychologists, subtracting out agreement due to chance, using Fleiss’ kappa. Also, find Fleiss’ kappa for each disorder.

Fleiss' kappa worksheet

Figure 1 – Calculation of Fleiss’ Kappa

For example, we see that 4 of the psychologists rated subject 1 to have psychosis and 2 rated subject 1 to have borderline syndrome. No psychologist rated subject 1 with bipolar or none.

Other Formulas

We use the formulas described above to calculate Fleiss’ kappa in the worksheet shown in Figure 1. The formulas in the ranges H4:H15 and B17:B22 are displayed in text format in column J, except that the formulas in cells H9 and B19 are not displayed in the figure since they are rather long. These formulas are:

Cell Entity Formula
H9 s.e. =B20*SQRT(SUM(B18:E18)^2-SUMPRODUCT(B18:E18,1-2*B17:E17))/SUM(B18:E18)
B19 κ1 =1-SUMPRODUCT(B4:B15,$H$4-B4:B15)/($H$4*$H$5*($H$4-1)*B17*(1-B17))

Figure 2 – Long formulas in worksheet of Figure 1

Note too that row 18 (labeled b) contains the formulas for qj(1–qj).

The p-values (and confidence intervals) show us that all of the kappa values are significantly different from zero.

Finally, note that in versions of Excel after Excel 2007, you can use NORM.S.INV instead of NORMSINV and NORM.S.DIST(H10,TRUE) instead of NORMSDIST(H10).

Worksheet Function

Real Statistics Function: The Real Statistics Resource Pack provides the following function:

KAPPA(R1, j, lab, alpha, tails, orig): if lab = FALSE (default) returns a 6 × 1 array consisting of κ if j = 0 (default) or κj if j > 0 for the data in R1 (where R1 is formatted as in range B4:E15 of Figure 1), plus the standard error, z-stat, z-crit, p-value and lower and upper bound of the 1 – alpha confidence interval, where alpha = α (default .05) and tails = 1 or 2 (default). If lab = TRUE then an extra column of labels is included in the output. If orig = TRUE then the original calculation for the standard error is used; the default is FALSE.

For Example 1, KAPPA(B4:E15) = .2968 and KAPPA(B4:E15,2) = .28. The complete output for KAPPA(B4:E15,,TRUE) is shown in Figure 3.

Fleiss kappa function results

Figure 3 – Output from KAPPA function

Data Analysis Tool

Real Statistics Data Analysis Tool: The Interrater Reliability data analysis tool supplied in the Real Statistics Resource Pack can also be used to calculate Fleiss’s kappa. To calculate Fleiss’s kappa for Example 1 press Ctrl-m and choose the Interrater Reliability option from the Corr tab of the Multipage interface as shown in Figure 2 of Real Statistics Support for Cronbach’s Alpha.

If using the original interface, then select the Reliability option from the main menu and then the Interrater Reliability option from the dialog box that appears as shown in Figure 3 of Real Statistics Support for Cronbach’s Alpha.

In either case, fill in the dialog box that appears (see Figure 7 of Cohen’s Kappa) by inserting B4:E15 in the Input Range, choosing the Fleiss’ kappa option, and clicking on the OK button. The output is shown in Figure 4.

Fleiss's kappa analysis tool

Figure 4 – Output from Fleiss’ Kappa analysis tool

Note that if you change the values for alpha (cell C26) and/or tails (cell C27) the output in Figure 4 will change automatically.

Examples Workbook

Click here to download the Excel workbook with the examples described on this webpage.

References

Cardillo, G. (2009). Algorithm for Fleiss’s kappa, MATLAB
http://www.mathworks.com/matlabcentral/fileexchange/15426-fleisses-kappa/content/fleiss.m

Wikipedia (2013) Fleiss’ Kappa
https://en.wikipedia.org/wiki/Fleiss%27_kappa

383 thoughts on “Fleiss’ Kappa”

  1. Hello Charles,
    thank you for your great work in supporting the use of statistics. It already helped me a lot 🙂
    I tried to use Fleiss Kappa from the Real Statistics Data Analysis Tool. But it won’t work for me. I Always get the error #NV, although i tried out to Change things to make it work.
    In my study i have three raters that rated students perfomance on the one hand with a dichotomous questionaire (yes/no) and on the other hand there was a Likert Skale (1-5) questionaire. For both questionaire i would like to calculate Fleiss Kappa. But both won’t work. I already deleted the rows when there was one rating of the 3 raters missing. But i still get the same error.
    What am I missing?

    Reply

      • Hi there. I also had the same problem with results coming out as errors. I’m not great with statistics or excel but I’ve tried different formats and haven’t had any luck. Did you find a solution for the people above?

        Reply

        • Hello Suzy,
          Yes. The correct format is described on this webpage, but in any case, if you email me an Excel file with your data, I will try to help you out.
          Charles

          Reply

  2. there is a problem with the B19 cell formula. I tried to replicate the sheet provided by you and still am getting an error

    Reply

    • I just checked and the formula is correct. It works perfectly well on my computer.
      What error are you getting?
      If you email me an Excel file with your data and results, I will try to figure out why you are getting an error.
      Charles

      Reply

  3. Thank you for these tools. I keep getting errors with the output however. I am trying to obtain interrater reliability for an angle that was measured twice by 4 different reviewers. I tried to use fleiss’s kappa but i wasnt sure how to structure the array. Either way, when I select 4 columns of data, I get an alpha of 0.05 but the rest of the table shows errors (#N/A). Any suggestions?

    Reply

  7. I would like to ask your assistance as i am trying to work on the inter-agreement of the rater on the items of the questionnaire. Following your formula of the Fleiss Kappa, but i cannot continue because of the command in the excel: =1-SUMPRODUCT(B9:B44:$H$9-B9:B44)/($H$9*$H$10*($H$9-1)*B46*(1-B46))…which is to get b, is not working. What can possibly wrong?

    Reply

  8. Hello!

    Thanks so much for this helpful tutorial. I am currently conducting research in which 10 raters evaluate a surgical training questionnaire. The raters select all themes that apply to a question (themes include: “blood supply”, “leg anatomy”, etc.). So, 10 raters can answer that a question addresses blood supply and nine raters can say that same question addresses flap reach. My current data sheet looks exactly like the one included as an example on this page, except the raters can select multiple diagnoses. I suspect that this affects the value of m in this scenario.

    Do you have any advice on how to proceed from this point?

    Reply

    • Hello James,
      This a great question, and I have tried to find an approach using existing techniques that I am familiar with to come up with a solution. The best approach that I can think of is to use Kendall’s W. If say there are 5 categories, then each rater gives a score to all the categories making sure that the sum of the ratings adds up to 1+2+3+4+5 = 15. Thus if a rater chooses only blood supply, he/she would give 15 points to blood supply and 0 to the other categories. If instead the rater chooses blood supply and leg anatomy, then he/she could give 7.5 points to each of these categories and 0 to the other categories (or if blood supply is more important, say 9 to blood supply and 6 to leg anatomy).
      See Kendall’s W
      Charles

      Reply

  9. Hello Charles,

    Thank you for this great tool.
    I would appreciate your help in interpreting some of my Fleiss kappa results. Here is a link to my sample excel sheet on Dropbox https://www.dropbox.com/s/irbrne86xq51970/fleiss-kappa-case1.xlsx?dl=0

    I have three annotators judging 597 question-answer pairs. Each answer can be judged as “direct”, “indirect”, or “incorrect” answer. The kappa scores that I got for kappa-all, kappa-direct, kappa-indirect, and kappa-incorrect are 0.383, 0.586, 0.292, and 0.1521, respectively.
    My question is: how can I interpret the relatively higher kappa score of 0.586 for kappa-direct. This phenomena of having the highest Fleiss kappa for kappa-direct is prevalent in any sample that I take out of my 2064 question-answer pairs. Please refer to the excel sheet in the link above for the kappa function parameters.

    Thank you

    Reply

  10. Dear Charles,
    Thank you so much for this wonderful tool! I am finding a lot of useful explanation here but I seem to get more confused every time.
    I have sets of medical images with 6 different features (thick borders, nodules, nests…). Each image is graded by the same 4 observers and they need to say whether or not they see the features in the images.

    I have 22 images, 6 features (present/absent) and 4 observers.
    From what I understand, categorical data (yes-no) and multiple raters calls for a Fleiss Kappa. I get 6 different kappa values, each assessing how strong my criteria is in my images. (Is that right)

    Then I repeat the same test with a different group of graders (students vs teacher) and I want to see which group is the best at identifying features. This is where it gets confusing for me.

    Thanks so much in advance for your help and for putting together this amazing website.

    Reply

    • Hello Sabrina,
      Glad that you are getting value from the website.
      Yes, you are correct: you can calculate 6 kappa values, one for each feature. If you code all the features together (e.g. number of features found, which is a number between 0 and 6), then you would have one value for kappa. This may or may not be helpful, depending whether the particular coding meetings your needs.
      Now let me try to answer the question you asked. The value of kappa simply tells you whether the original 4 observers tended to agree. This may or may not be useful in your task of comparing teachers with students. You still don’t know for sure what the “gold standard” is for this identification task. If, for example, you see that the 4 observers are largely in agreement and these observers are considered experts, then you can use their results to set the standard, creating a single set of ratings based on the ratings from the experts.
      To compare the evaluations of teachers with students, you can calculate the kappa value for experts vs teachers, and then calculate a second kappa value for experts vs. students. The higher kappa indicates more agreement with the experts.
      You could probably use a t test instead to see which group scores better or even use Bland-Altman.
      These are some ideas for how to proceed. I am sure there are others.
      Charles

      Reply

  11. Hi Charles, first of all – thank you for this extremely helpful site and the clear explanations!

    I am integrating the Fleiss Kappa into my software, which is a labelling software for AI traing. So, once that is done, I get an idea about the reliability of my datasets.

    Since I need to label hundred thousand of images I have a pool of freelancers that are categorizing images, generally about 8-10 build a group for one trait, and each image gets a max. of 4 votes. I have 7 categories from extreme strong to extreme weak.

    I realised that the quality of the ratings is extremely dependent on the individual. And, moreover, there is a learning effect with the time: the observers become better.

    So, this is similar to Maikes question from 2016, but a group comparison (like beginners vs. experienced) is too vague.

    What would be the best concept do achieve such a score?

    Best, Peter

    Reply

    • Hi Peter,
      Since the ratings are on an ordered scale (extreme strong to extreme weak), you shouldn’t use Fleiss’ kappa since it only deals with categorical ratings and would ignore the ordering. In this case, Gwet’s AC2, Krippendorff’s Alpha or ICC would be better choices since they handle ordered categories.
      In your question, “What would be the best concept to achieve such a score?”, I don’t know what score you are referring to. What exactly are you trying to measure? The difference in ratings between the experienced vs beginners?
      Charles

      Reply

      • Hi Charles, okay, thanks, i´ll try to use the other choices.
        And yes, my question was missing, sorry 😉

        I want to measure the performance of a single rater (unexperienced freelancer) over time in comparison to a group of trainers (educated trainer) in order to see his learning success.

        In some datasets i have two experienced trainers and two freelancers in others i have only one trainer and three freelancers.

        Oh, and, of course, i have timestamps in my collected records, so i can build time-based datasets, like monthly or quarterly.

        Reply

        • Hi Peter,
          If you believe that the experienced trainers give more accurate ratings than the inexperienced ones, you can always conduct a t test (or something similar) to see whether there is a significant difference between the average ratings between the groups. Bland-Altman may be another option.

          Charles

          Reply

  12. hello
    I am working on a translation of a clinician rating scale
    there is only one item with 7 point likert scale
    for each patient there are two raters, these raters are not fixed thought the number of raters are fixed . after discussing illness history of a patient each rater is asked to rate the patient’s condition on these 7 points.
    there are 40 patients in total with 2 raters for each patient
    which type of analysis would be suitable I am using SPSS 20 and 25

    Reply

    • Hello Muhammad,
      If I understand correctly there are 40 patients, each rated by two raters (although the actual raters may vary) using a 7 point Likert scale.
      Fleiss’ kappa would be a good choice since the raters may vary, but Fleiss’ only deals with categorical ratings and so with a Likert scale this is not a good choice.
      I would therefore suggest using Krippendorff’s alpha or Gwet’s AC2. These are supported by Real Statistics. SPSS probably supports one or both of them, but I am not sure about this. Some version of ICC might also be appropriate.
      Charles

      Reply

  13. Hi Charles,
    I would like to ask you two things:
    – I have a questionnaire y / n (21 questions) with 3 examiners, 20 cases, I have calculated the k for each single question. Is it wrong to use Davies-Fleiss’s theory of the average value of pe? from my analysis it seems the only way to represent the variability of the answers with dichotomous variables.
    if k = 1, the upper value can be greater than 1?
    Thanks in advance.

    Reply

    • Hi Livia,
      I am not familiar with the Davies-Fleiss measurement, and so I am not able to answer your question. I will add this to my list of possible future enhancements.
      Charles

      Reply

      • Dear Charles,
        thanks for the answer to the first question.
        Do you know how I can solve the problem of the confidence interval that exceeds the value 1 when k = 1?

        Reply

        • Dear Livia,
          The confidence interval should not exceed 1. If so, then I would suggest that you change the value to 1. I would first make sure there was no mistake made. If you send me an Excel file with your data and results, I will check this for you.
          Charles

          Reply

  14. Hello,

    Thanks so much for the information. My question is: is it possible/ does it make sense to calculate fleiss’s kappa for one subject. So for example 18 raters, with yes/no answers, for one question. The lead of the project I am working on would like to have the kappa value for each question to determine which question has the highest inter-rater agreement. When I attempt to implement this in r for one question at a time, I get strange results. (any questions with 100% agreement get an NaN kappa value and all the others have the exact same negative value). Thank you!

    Reply

    • Patricia,
      No, you can’t just have one question. If you have more than 3 questions, then you can calculate Fleiss’ kappa leaving out one of the questions. Yoy can do this for each question. This would give you some idea of the contribution of each question.
      Charles

      Reply

  15. Thanks so much for you very helpful and user friendly page here! I have a question which I know might be stupid, but I am a doctor of literature and not maths… What does the 2 implicate in the formula of the standard error for κj in Definition 1: Fleiss’ Kappa?

    Thanks for your time!!

    Reply

  16. Dear Charles Zaiontz,

    Thank you for this amazing website and detailed explanations.

    I am trying to examine inter-rater reliability for my survey but I got a little bit confused.
    I have 280 different food pics (stimuli) and 50 (raters) different people rated these pics if they are low, average or high calorie (3 levels). So, 280 pictures were rated 50 times from different participants into 3 different calorie groups. I want to understand if I can statistically say that one food stimuli was considered as low calorie with consensus among raters by using Kappa. Can I use Fleiss’ Kappa or should I use something else?
    Thank you so much in advance

    Reply

    • Emre,
      Fleiss’s Kappa will determine whether or not there is a high level of agreement between the 50 raters based on the 2800 pictures using all three categories (not just low calories). Fleiss’s Kappa won’t take into account the order of the three ratings. To take this order into account, you should use Gwet’s AC2.
      Charles

      Reply

  17. Dear All,
    What kind of kappa can i use to make the table like this by SPSS?

    Table 1. Comparison of Allplex Respiratory Panel 1/2/3 and Anyplex II RV16 in the detection of a single respiratory virus
    Kappa value Agreement
    Observed kappa (95% CI) Positive Negative
    % (95% CI) No.* % (95% CI) No.
    1 AdV 0.78 (0.64-0.92) 70.8 (50.8-85.1) 24/19 99.5 (98.1-99.9) 376/381
    2 229E 0.97 (0.90-1.00) 93.8 (71.7-98.9) 16/15 100 (99.0-100) 384/385
    3 NL63 0.89 (0.78-1.00) 85 (0.64-0.94) 20/18 99.7 (98.5-100) 380/382
    4 OC43 0.93 (0.82-1.00) 100 (77.2-100) 13/15 99.5 (98.1-99.9) 387/385
    5 FluA 0.94 (0.87-1.00) 90 (69.9-97.2) 20/18 100 (99.0-100) 380/382
    6 FluB 1.00 (1.00-1.00) 100 (72.2-100) 10/10 100 (99.0-100) 390/390
    7 HBoV 0.83 (0.73-0.93) 90.3 (75.1-96.7) 31/35 98.1 (96.1-99.1) 369/365
    8 HEV 0.70 (0.45-0.95) 54.5 (28.0-78.7) 11/6 100 (99.0-100) 389/394
    9 MPV 0.88 (0.77-1.00 100 (80.6-100) 16/20 99 (97.4-99.9) 384/380
    10 HRV 0.86 (0.78-0.93) 94.3 (84.6-98.1) 53/61 96.8 (94.4-98.2) 347/339
    11 PIV1 1.00 (1.00-1.00) 100 (51.0-100) 4/4 100 (99.0-100) 396/396
    12 PIV2 1.00 (1.00-1.00) 100 (72.2-100) 10/10 100 (99.0-100) 390/390
    13 PIV3 0.57 (0.43-0.71) 95.5 (78.2-99.2) 22/48 92.9 (89.8-95.0) 378/352
    14 PIV4 0.67 (0.05-1.00) 100 (20.7-100) 1/2 99.7 (98.6-100) 399/398
    15 RSVA 1.00 (1.00-1.00) 100 (67.6-100) 20/20 100 (99.0-100) 380/380
    16 RSVB 1.00 (1.00-1.00) 100 (83.9-100) 8/8 100 (99.0-100) 392/392
    Total 0.78 (0.72-0.85) 93.2 (89.4-95.7) 84.7 (78.0-89.6)
    “*No.: Number of results for each virus in AnyplexII RV 16/Allplex Respiratory Panel 1/2/3.
    Abbreviations: AdV, adenovirus; 229E, coronavirus 229E; NL63, coronavirus NL63; OC43, coronavirus OC43; FluA, influenza A virus; FluB, influenza B virus; HBoV, human bocavirus 1/2/3/4; HEV, human enterovirus; MPV, human metapneumovirus; HRV, human rhinovirus A/B/C; PIV1, parainfluenza virus 1; PIV2, parainfluenza virus 2; PIV3, parainfluenza virus 3; PIV4, parainfluenza virus 4; RSVA, respiratory syncytial virus A; RSVB, respiratory syncytial virus B.”

    Reply

    • Jean,
      Generally with two raters and categorical data you can use Cohen’s kappa to test for agreement between the two raters. This data doesn’t appear to be categorical, but numerical. ICC might be a reasonable choice, but I don’t understand what kind of data you have, and so I can’t really say for sure.
      Charles

      Reply

  18. Hello Charles,

    just wondering If I can use kappa with five point likert scale data? and can I use it with missing data?

    thank you

    Reply

  19. Hello Charles,

    Thank you for the great statistic tools and information!
    I have a question about Fleiss’ Kappa. I have about patient specimens read by three pathologists, and rating of each specimen is either positive for a high grade lesion or negative for high grade lesion. In the past , I’ve used the “interrater reliability” tool and calculated the Fleiss’ Kappa for several group of patients with certain diagnosis (according to a Gold Standard diagnostic method), and had no problem. However, For one group of patients (about 100 of them), all the doctors agreed that they have high grade lesion, so I was expecting to see a perfect agreement, and Fleiss’ kappa of 1, but when I tried to use the “interrupter reliability” tool, no Kappa was calculated (says there is a error in the formula). Just to play with it a little bit, I changed a few readings to “negative” and see what happens, the test did calculate a kappa this time, but it was a negative value. I’m not a statistic person, and now is very confused. Any suggestions? Thank you very much for your help in advance!
    My data was listed like this:

    Case# positive negative
    1 3 0
    2 3 0
    3 3 0

    until case #100

    Reply

    • Susan,
      Unfortunately, this sort of strange behavior does occur when using Fleiss’s Kappa. I suggest that you use Gwet’s AC2 instead if you want to avoid these sorts of counter-intuitive results.
      Charles

      Reply

      • Charles,

        Thank you so much for your quick reply!
        I tried Gwet’s AC2, and it worked really well. I do have another question: is there a way to compare agreement coefficients of two groups (say one AC2=0.8, and the other AC2=0.4) for statistic significance? I feel I’m in way over my head, but thought I’d ask just in case there is a function in there that I could use easily. Thank you so much for your help!

        Susan

        Reply

        • Susan,
          You can calculate the confidence interval for each group and see whether these confidence intervals overlap. I think this approach might be useful to addressing the issue that you have presented.
          Charles

          Reply

  20. Hello,

    Thank-you for the great information! I would like to perform a Fleiss Kappa test to evaluate 3-4 inspectors rating coins for defects. I have a total of 23 categories of defects (including a category of “no defect”). Any tips or advice before I start? Thanks!

    Reply

    • Theresa,
      Since you have a great many rating categories, I hope that each inspector rates a lot of coins. Also, there are other approaches, Gwet’s AC2 and Krippendorff’s alpha, that can be used.
      Charles

      Reply

        • Lara,
          This usually means that you have not installed the software. See installation instructions on the same webpage from where you downloaded the software. When the software is correctly installed you should see RealStats and Solver on the list of addins when you press the key sequence Alt-TI.
          Charles

          Reply

  22. Hi. Thank you for this information. I have a question.

    Can I use Fleiss’ Kappa with 12 different items and “yes” or “not” as the possible answers? I have 5 raters. They all will rate the same items.

    Thanks

    Reply

  23. Hi Charles,
    Thank you for this webpage. Can I use this method for only two raters in a similar scenario to your example? Will this give me similar results to Cohen’s kappa? More specifically, I want to calculate overall kappa and I’m not sure this is possible with Cohen’s kappa.
    Thanks!

    Reply

  24. Hello.
    I realize this may be a little late in the game, but I have a survey that I designed to obtain consensus on various aspects of a topic. This survey has three categories (agree, disagree, modify) and roughly 100 statements (cases). I have 41 raters who have take the survey.
    Would Fleiss’ kappa calculation be appropriate for this? I need to establish if there is agreement between my raters regarding the various statement.
    Thank you.
    Aina

    Reply

  25. The interpretation of Fleiss’ Kappa comes from this book:
    Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics 1977;33(1):159-74.
    <0 Poor agreement
    0.0-0.20 Slight agreement
    0.21-0.40 Fair agreement
    0.41-0.60 Moderate agreement
    0.61-0.80 Substantial agreement
    0.81-1.0 Almost perfect agreement

    Reply

  26. Hi there, thank you for this helpful page!
    I am wondering, what is the reason why you cannot simply calculate Cohen’s kappa for each pair or raters and find the mean of those values to give an overall represetation of agreement?
    For example, I am looking at this paper currently:
    https://www.ncbi.nlm.nih.gov/m/pubmed/19649750/
    Choen’s Kappa values reflecting inter-observer reliability among 4 readers ranged from 0.39 to 0.79, and were averaged to give a mean 0.60, taken as a overall index of reliability.
    Should Fleiss’ Kappa have been used ideally?

    Reply

  27. Hi Charles,
    I could be wrong but it appears your formula for SE in figure 2 (cell H9) is missing an array term in the sumproduct function. In the equation in the text, you write the second term in the numerator of the square root as:

    q_j*(1-q_j)*(1-2*q_j)

    yes the sumproduct in figure 2 is written as:

    sumproduct(B18:E18,1-2*B17:E17)

    where row 17 is q_j and row 18 is 1-q_j

    without this extra term, the radicand can become negative and the SE incalculable.

    Hoping I’m right on this.

    Reply

    • Hi Charles I am trying to use Fleiss K but I have an issue using formula for cell H9.
      I wrote : B24*RACINE(SOMME(B22:D22)^2-SOMMEPROD(B22:D22,1-2*B21:D21))/SOMME(B22:D22) but it’s not working excel says it’s a problem with “D22,1-2” do you have an idea about how to fix it?
      Thank you very much for your help !

      Reply

  28. Thank you, Charles. Will it be possible for me to send you my data and for you to have a look at it on how best to represent my data?

    Reply

  29. Hi Charles,
    I have completed a survey where the intention is to measure level of agreement on the diagnosis of 4 cases by 57 raters.
    In each case, there are 4-5 possible answers given, but the aim is only to score them as 1 is rater 1 and rater 2 agree on the same diagnosis.
    I understand Cohen’s kappa would only work for 2 raters. Would Fleiss’ kappa work in this instance, and how might I compute this (Is there a calculator I can use online)?
    Thanks a lot.

    Reply

      • Hi Charles,
        I tried using Cohen’s kappa for a few cases manually at first and averaged out the kappa for each case. For 4 cases, it would as such:
        Raters
        1 vs 2
        1 vs 3
        1 vs 4
        2 vs 3
        2 vs 4
        3 vs 4
        That would work out to be 7 pairs.

        If the diagnosis was the same, I scored it as 1; if it was discordant I scored it as 0.

        For each case, I would then score the count as a fraction. Eg. If there was perfect agreement for 5 pairs, the count would be 5/7.
        I would then add the fractions from each of the 4 cases and divide by 4.

        However, I realized this wasn’t going to be possible for 56 raters!
        Also, the values I worked out seemed to grossly underestimate the level of agreement.

        From your explanation, Fleiss kappa seems to make more sense to me for my data. But it doesn’t seem to require a rater 1 vs 2 agreement, hence I am not quite sure how best to approach this and would greatly appreciate any advice.

        Joan

        Reply

        • Joan,
          The typical approach is to use as input data the ratings made by each rater on each subject (independently of the other raters). The interrater measurement then calculates the degree of agreement between the raters. This makes things less complicated than the approach you are envisioning. You can use Fleiss’ kappa with 4 raters (or in fact any number of raters > 1) provided the ratings are categorical, i.e. not Likert scores (e.g. ratings from 1 to 5) or numeric values (ratings of 2.67 or 3.63, etc.). If you need non-categorical ratings, then there are other measurements available — e.g. Interacorrelation (ICC), Gwet’s AC2, Krippendorff’s alpha or Kendall’s W. All of these are described on the Real Statistics website.
          Charles

          Reply

  30. I am conducting a content analysis pilot study on 23 novels. There are five coders and 16 personality traits. The traits are not mutually exclusive and the coders are marking them as either yes the trait was exhibited by the character or no it was not.

    What is the best way to test inter coder reliability?

    Reply

    • Lona,
      I don’t have a definitive answer for you, just some ideas.
      Fleiss’ Kappa handles the case where each rater assigns a rating for one of the traits. For your problem you have multiple traits and so possible approaches are: (1) simply report one Fleiss’ kappa measurement for each of the 16 traits, (2) combine the Fleiss’ kappa measurements in some way (average, max, etc.), (3) use some complicated coding that handles all 16 traits (e.g. a vector of 16 elements consisting of zeros and ones).
      Approach 1 is simply and may be the best, but it doesn’t give ratings that handle all the traits simultaneously. Approach 2 seems pretty arbitrary, but is probably the one most often used. Approach 3 seems reasonable, but then you need to come up with some way of ordering the vectors or determining distance between vectors that captures similarity of ratings; in this case you wouldn’t use Fleiss’ kappa (which is restricted to categorical data) but Gwet’s AC2 or Krippendorff’s alpha or something similar.
      I don’t know whether this issue is covered in the following book, but it covers interrater releiability:
      Handbook of Inter-Rater Reliability, 4th Edition by Gwet
      Charles

      Reply

  31. Hi Sir,
    Thank you for the website. I’ve downloaded the resource pack, and tried to do the Fleiss Kappa analysis following the instruction, but got the error message saying “compile error in hidden module:correlation”. Could please help me to solve this problem? Thanks a bunch!

    Reply

    • Susan,

      Here are some steps for diagnosing or potentially resolving this problem.

      1. Try using one of the Real Statistics functions. In particular, enter the formula =VER() and see whether you get an error, in which case, the software has not been installed correctly
      2. Solver has not been installed. When you choose the Add-Ins option from the Tools menu, do you see RealStats and Solver in the list of addins with a check mark next to them?
      3. See Hint 2 at https://real-statistics.com/appendix/faqs/disappearing-addin
      4. The problem might be with the Trust Center settings. Click on Options from the File ribbon and then choose the Trust Center option on the left side. Next click on Trust Center Settings …. Next click on the Macro Settings option on the left side and make sure that it is Disable all Macros with Notification. Also click on the Trusted Locations option on the left side and click on the Add New Location… button to add the folder that contains RealStats-2007 folder as a trusted location.
      5. Try opening a blank Excel worksheet and press Alt-TI. Uncheck the RealStats addin and close Excel. Now open a blank Excel worksheet and press Alt-TI. This time check the RealStats addin and now try to use the Fleiss’ Kappa analysis tool.

      Charles

      Reply

      • Thank you so much for your quick reply! Sorry I wasn’t clear, I’m using a MacBook, and Excel 2011. Does that make any difference? I don’t see “real statistic functions”, only the” data analysis tool”, and I was trying to use the “interater reliability” function in the “correlation” tab.
        Anyway, I will also try PC, and see if that will work. Thank you so much for your help!

        Reply

          • Hi Charles,
            Thank you so much for your help. =VER() returned “5.0 Excel Mac”. I also got the Kappa function to work, which will return a single number. However, when I tried to input all the parameters to get an output like Figure 3, it only returned a word “kappa”. On the bottom of the window where you put in the parameters, I can see part of the result (Kappa, s.e., but then got truncated, so I could not get the Z, p etc). Could you think of a reason for this? I feel like I’m very close to getting it to work properly, just not quite yet. Thank you, I really appreciate your help!

          • Sorry, forgot to say:

            The parameters I put in were like this:
            rg=E2:G18 (range of my data)
            col=3 (I have 3 categories)
            lab=TRUE (I’m not sure about this, just followed theexample, which said if I want to see a result in Figure 3, lab=TRUE, am I right?)
            alpha=0.05
            tail=2
            orig=TRUE (I’m not sure what this is either or what else I could potentially chose to put in).
            I tried to define my output area as 1 cell, a 1×6 area, a 2×6 area. None of them worked, all I saw was a word “kappa” in the first cell.
            Any suggestion would be great appreciated.

          • Hi Charles,

            Just want to let you know, I downloaded a PC version to my old old PC, it’s working. Thank you very much for all your help.

  32. Great article, I tried Fleiss Cappa and it worked. An excellent and easy to use software as well.
    Just a question- I am doing IRR for a Clinical Audit Tool with 9 assessors. Each of them will assess if the clinical records done by clinicians are good, average or bad- so three categories. Will I be using one tail or 2 tail in this case?

    Reply

      • Thanks Charles,

        I did the analysis, and it worked well for 9 out of 10 items I was assessing. it did not work for one item though: I have the data below:
        Good Average Poor Non Resposne
        9 0 0 0
        9 0 0 0
        9 0 0 0
        9 0 0 0
        9 0 0 0
        9 0 0 0
        9 0 0 0
        9 0 0 0
        9 0 0 0
        9 0 0 0
        9 0 0 0
        9 0 0 0
        9 0 0 0
        9 0 0 0
        9 0 0 0
        9 0 0 0
        9 0 0 0
        9 0 0 0
        9 0 0 0
        9 0 0 0

        As all nine assessors rated good for all samples, it should be showing as +1?
        But the result was as shown below:
        Fleiss’s Kappa

        alpha 0.05
        tails 2

        Total Good Average Poor Non Resposne
        #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE!
        #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE!
        #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE!
        #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE!
        #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE!
        #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE!

        Could you please help?
        Thanks

        Reply

        • This is an oddity of many of these measurements. Since the variance for your data is zero, the calculation of the statistic probably involves division by zero and so the statistic is undefined. In any case, you can assume that you have complete agreement and don’t really need to calculate kappa. You can treat it as if the value was +1.
          Charles

          Reply

  33. Hello Charles,

    so I have a question. I have an open card sorting with 10 raters, 23 items and 2 categories.
    It’s 230 ratings in total, and in 225 out of the 230 cases, the raters assigned the same category.
    Using the add-in i get a Fleiss Kappa of 0,92067698.

    However, the p-value always amounts to 0. How is that possible?

    I also tried changing the numbers so there would be more volatility (e.g. set 225 down to 180 and the Fleiss kappa shrunk but the p-value is still 0?

    Maybe it’s a problem since I am using a German Excel version?
    The regular Cohen’s Kappa calculation also doesnt work for me
    Tyvm!

    Reply

    • Patrick,
      If you send me an Excel file with your data and calculations I will try to figure what is happening.
      The German version shouldn’t give a different answer from the US version (unless there is a problem with the decimal symbol).
      You can find my email address at Contact Us.
      Charles

      Reply

  34. Hi Charles,
    Thank you so much for this website.
    I have analyzed the inter- rater reliability for 5 raters on 34 items. the variables were dichotomous (correct, wrong). the Average pairwise percent agreement was 82.4%. However, the Fliess kappa was 0.32 and Krippendorff’s Alpha was 0.32 as well. Actually, I am frustrated, and I do not know how to report my data. or if there is away to correct the kappa.
    your help is much appreciated.
    Enas

    Reply

    • Enas,
      It looks like it is easy to report your results, although it seems like you don’t like the result.
      The reason for doing analysis is to find out whether or not your hypotheses are correct. A negative result is still a result.
      Charles

      Reply

  35. Hi Charles,
    This has been very useful so far. Thank you.

    My work is similar to your example but there are the following differences:
    -instead of 4 psychiatric diagnoses, there are 2 columns: Absence and Presence.
    -instead of 12 patients, there are 6 patients.
    -instead of 6 raters, there are 15 raters.

    I have two queries:
    1. In one part of my research, all 15 raters agree on ‘Presence’ for every patient. However, Fleiss’ kappa can not be calculated because (if you follow your manual method) you end up dividing by 0. This is not possible. What should I do?

    2. In another part, 15 raters agree on ‘Presence’ for the first 5 patients. For the final patient, 14 agree on ‘Presence’ with the remaining rater stating ‘Absence’. I would expect the kappa value to be relatively high. However, it is negative.

    This is very confusing and I would be very grateful if you could help.

    Thank you.

    Reply

    • Joseph,
      One of the problems with Fleiss’ Kappa is that you can get some counter-intuitive, esp. in extreme cases. My understanding is that Gwet’s AC2 measurement addresses some of these problems. The next release of the Real Statistics software will include support for Gwet’s AC2. Regarding your specific questions:
      1. If all raters agree, simply report 100% agreement (don’t bother with Fleiss’ Kappa)
      2. Once again with this level of agreement, you should simply report that you have 100% agreement except in one case.
      Charles

      Reply

  36. Hi Sir,

    I would like to ask how can I assess the agreement between an isolated rater (master rater) VS a group of say 10 raters. The variables are ordinal, like No Disease, Mild Disease, Moderate Disease, Severe Disease.

    Thanks in advance for your reply!

    Reply

  37. Hi Sir,

    Could you assist me with the following?

    My response outputs from my 4 raters are non-categorical, for e.g ” 52 years, 53 years” . Initially, I manual group them into “Yes” and “No” before using SPSS to calculate the Kappa Scores. But, how do I go about in calculating the Kappa score for them without manual grouping the responses (Just by putting the raw data into SPSS)

    Thank you!

    Reply

    • Sorry Xinru, but I don’t completely understand your question. If you have non-categorical data, then Fleiss’ kappa is probably not the right tool to use. Perhaps ICC would be better.
      Charles

      Reply

  38. Hi Charles,

    Many thanks for producing this, it’s very helpful. I wonder if you could help me with a question. I’m trying to calculate the degree of interrater reliability between three raters when screening research papers for inclusion in a systematic review. The three raters have the option to include or exclude each of the 20 papers. I think I’ve followed you instructions for formatting correctly. The raters all agreed on 18 papers. On the other two there was a 2 to 1 split (ie. two raters said include, the other exclude).

    When I input that, I get the following result:

    Kappa = 0.86 (p <0.05), 95% CI (0.599, 1.118)

    I noticed that the upper CI value is greater than 1. I assumed that the value would be bounded at 1 because that would represent perfect agreement. Have I misunderstood something or made an error?

    Many thanks
    Rob

    Reply

  39. Hello, thank you very much for sharing them.
    Could you do me a favor?
    1. As you know, Cohen’s kappa has set of criteria, it is: less than 0% no agreement, 0-20% poor, 20-40% fair, 40-60% moderate, 60-80% good, 80% or higher very good. How about Fleiss’s kappa, are they the same?
    2. What is the difference between Cohen’s kappa and Weighted Cohen’s kappa?
    3. I need to measure the agreement between 8 raters. Is it possible if I use Cohen’s kappa for each couple of rates and then I measure the medium of all the kappa?
    4. Is there any software of application to measure Fleiss’s kappa ( Ex: Something like spss or medcalc..)
    Thank you so much for helping me!

    Reply

    • Linh,
      1. You can use the same criteria as for Cohen’s kappa, although there isn’t universal agreement about these criteria.
      2. See Weighted Kappa
      3. You can do this, but it is not clear how you would interpret the result
      4. The Real Statistics software calculates Fleiss kappa. I would think that SPSS and Medcalc do as well, but I cant say for sure since I dont use these tools.
      Charles

      Reply

  40. Hi
    I have a problem taking results from the reliability testing. I have 3 columns with marks (1,2,3) from 3 raters and when i run the Fleiss’s kappa on these values
    rater1 rater2 rater3
    1 1 2
    3 3 3
    1 1 1
    2 2 2
    3 3 3
    3 3 3
    2 2 1
    1 1 2

    I get this table

    Fleiss’s Kappa
    alpha 0,05
    tails 2

    Total rater1 rater2 rater3
    #N/A #N/A #N/A #N/A #N/A
    #N/A #N/A #N/A #N/A #N/A
    #N/A #N/A #N/A #N/A #N/A
    #N/A #N/A #N/A #N/A #N/A
    #N/A #N/A #N/A #N/A #N/A
    #N/A #N/A #N/A #N/A #N/A

    please help if possible!

    Reply

    • This is not the correct format. Each role is a different rater and each column is a different category. The sum of the values in each row must be the same across all the rows.
      Charles

      Reply

    • I am sorry got it wrong! I had to sum the same marks and make a new table like that. (Please correct me if i am wrong!)
      mark1 mark2 mark3
      2 1
      3
      3
      3
      3
      3
      2 1
      2 1
      Thank you for the tools anyway!

      Reply

      • Kostas,
        This looks good, although when I see it on my computer all the columns are shifted left — in particular, there are no values for Mark3. You would have had to insert zeros for blank values, but this should not be a problem on the Excel spreadsheet.
        Charles

        Reply

  41. Data I sent earlier may be confusing. Please calculate Fleiss kappa and provide worksheet for following data-
    A 70 3 2 4

    B 2 44 5 0

    C 3 6 29 1

    D 5 1 1 24

    Reply

  43. Hello Charles,

    Unbelievably helpful…thank you! However, I am getting very low kappa’s for several surveys that we are making and I have read about this paradox when there is very high agreement (skewed distribution). Can you take a peek at our spreadsheet to ensure it is correct. It reflects 10 dichotomous ratings by 10 people about the understanding of survey items (first column). They are in very high agreement. Is there a way to handle this and way to report the kappa (or ranges) that is meaningful? Blue rows were not included in the analyses. I truly appreciate any insight that you can provide.

    Reply

    • Pick,
      No this isn’t the correct calculation. The main problem is that your columns correspond to the raters instead of the rating categories. Also the sum of the values in each row should be the same.
      Charles

      Reply

  45. Hi Charles.

    My research consists of 6 categories (Strongly Agree, Agree, Slightly Agree, Slightly Disagree, Disagree and Strongly Disagree) , 27 items, and 9 raters. Below are the results based on this article:
    m=9
    n=27
    Pa=0.322016461
    Pe= 25.28172394
    kappa=1.027921557
    se=0.018256452
    z = 56.30456314
    p-value = 0

    The kappa value is 1 which means excellent agreement but the z-value is so high. Is there something wrong based on the results? Thank you very much.

    Rose

    Reply

  46. Dear Charles,

    Thanks for sharing this! Im having trouble with dichotomous variables and 4 raters. Is there any option to calculate an ICC or Fleiss’ Kappa with dichotomous variables?

    Reply

  47. Thank you for this information on Fleiss Kappa.
    I am still having difficulties in conducting the Fleiss Kappa. I have 2 raters that evaluated over 1000 events for 3 different evaluation categories. The raters can only use 1 category out of the 3 to rate an event. I cannot do a Cohen Kappa because more than 3 evaluation category so I was doing an agreement score between the 2 raters but I have been told to do instead a Fleiss Kappa. I have organized my Excel table where for each event the evaluation category is 0 if no agreement and 1 if the 2 juges agree. So for each event you will have either three scores as 1 (if agreement) or two scores as 0 and one score as 1 (if disagreement). I wanted to do a Fleiss Kappa in SPSS or even Excel but I either way I cannot find how. Thank you in advance for your help with this.

    Reply

  49. hello,
    I need your help please regarding the calculation of kappa for a study. I have 5 raters for 13 articles. the rate is mainly based on scores from 1 to 5. I want to check the reliability by calculating kappa for each rater and overall.

    Reply

    • Simone,
      Kappa is a measurement of the overall differences between raters. You don-t calculate a kappa value for an individual rater.
      The way to calculate Fleiss’s kappa is shown on the referenced webpage.
      Charles

      Reply

  50. Charles,
    I am conducting a controlled test in which I have 30 evaluators and 10 pairs of samples. I am providing a sample pair to an evaluator to review and determine if the 2 cards are the same or different. Within the 10 pairs I have the 6 pairs that are different and 4 are the same. I know the standards and controls.
    My null hypothesis is that the cards are the same.
    My alternate hypothesis is that the cards are different.

    How would you recommend analyzing the data? One set? Separated?
    In Minitab using 1 set I am obtaining a p value of 1.0 in the Fleiss’ Kappa Statistics section and negative Kappa values.

    Fleiss’ Kappa Statistics

    Response Kappa SE Kappa Z P(vs > 0)
    Different -0.310712 0.05 -6.21425 1.0000
    Same -0.310712 0.05 -6.21425 1.0000
    Thank you in advance!

    Reply

    • Ben, regarding whether you create one Fleiss’ Kappa or two (one for the cards that are different and another for the cards that are the same), this really depends on what you are trying to show. Either can be useful.
      I don’t understand why you need to set null/alternative hypotheses or why you have chosen these hypotheses.
      Charles

      Reply

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