Cronbach’s Alpha is the most commonly used statistic for determining the internal consistency of measurements, such as items in a questionnaire, exam, or survey. It is equivalent to performing the split-half methodology on all combinations of these items.
Topics
- Basic Concepts
- Real Statistics Support
- Hypothesis Testing and Confidence Intervals
- Power and Sample Size
- Handling Missing Data and Not Applicable Entries
- Proof of Main Property
References
Tavakol, M., Dennick, R. (2011) Making sense of Cronbach’s alpha. International Journal of Medical Education
https://www.ijme.net/archive/2/cronbachs-alpha.pdf
Gliem, J. A., Gliem, R. R. (2004) Calculating, interpreting, and reporting Cronbach’s alpha reliability coefficient for Likert-type scales
https://scholarworks.indianapolis.iu.edu/server/api/core/bitstreams/976cec6a-914f-4e49-84b2-f658d5b26ff9/content
Newsom, J. (2017) Empirical estimates of reliability: Cronbach’s alpha
https://web.pdx.edu/~newsomj/pmclass/empirical%20estimates%20of%20reliability.pdf
Trizano-Hermosilla, I., Alvarado, J. M. (2016) Best alternatives to Cronbach’s alpha reliability in realistic conditions: congeneric and asymmetrical measurements
https://www.frontiersin.org/journals/psychology/articles/10.3389/fpsyg.2016.00769/full
Hi Charles,
I am looking for some guidance – – I have administered a pre-/post- survey, using a 5 point likert scale. Response prediction was a one-tailed shift, and this was true. Sample size was only 32, and most respondents shifted from a ‘3’ to a ‘2’ or ‘1’, so not a huge shift, but one that was pretty uniform. There were about 6 that did not shift at all. Although the shift was evident, my paired sample ttest returns a very high p-value, indicating no statistical significance. I am wondering if I should use a different analysis approach?? little out of my depth…
Kate,
Can you send me the data so that I can understand the situation better? See Contact Us for my email address.
Charles
Hi Charles,
I’m using a likert scale 1 to 5, 15 questions as feedback about facebook and moodle. Same set of questions apply to both facebook and moodle given to the same students (21 students). What is the best and proper approach? Seems like I cannot use the 0/1 coding. Please advice.
Depending on what you are measuring, you might need to compute two Cronbach’s alphas, one for moodle and the other for facebook. You can use the Likert scale as input to Cronbach’s alpha.
Charles
Hi Charles,
If the response is 1/0 the formula is …=(k/(k-1)…
if the response is 1, 2, 3, 4, 5…what would be the formula?
please advice
Tobias,
Sorry, but I don’t know which formula you are referring to. The formula that I use for Cronbach’s alpha is the same for dichotomous values as for Likert values.
Charles
I designed a 7th grade science test with 30 multiple choice items as part of an experimental investigation. Each question has four alternatives. Part I consists of 10 questions about the scientific method; Part II consists of 15 questions on the structure and organization of organisms, and; Part III consists of 5 questions about taxonomy. My question is: When I calculate reliability, should I calculate three separate Cronbach alphas (one for each part), or only one overall Cronbach’s alpha for the entire test? Also, is using the 0/1 coding (incorrect/correct) the correct procedure?
I appreciate your input and guidance.
Marilyn,
Since it looks like you are testing three different concepts, you should calculate three separate Cronbach alphas. The 0/1 coding (incorrect/correct) is correct.
Charles
Hi!
I would like to know if I can conduct cronbachs alpha on my own questionnaire?
For example, my questionnaire would be like this:
1. Advertising through tv or radio creates brand awareness.
2.Internet marketing creates brand awareness.
Then this would be in the form of a likert scale. 5-strongly agree then 1-strongly disagree.
Thanks for the help!
Pam,
Sure, you can use Cronbach’s alpha to test such things. It is important that if you are testing multiple concepts that you create a Cronbach’s alpha score for each concept based on the questions that relate to that concept.
Charles
For example,
there would be concepts about advertising, personal selling, sales promotion, and public relations. But this would be in just one questionnaire. Should i conduct cronbachs alpha separately for each concept?
Thanks!
Yes, you should conduct a separate Cronbach’s alpha for each concept.
Charles
May I ask something else, please?
1. If someone has a pre-post design with 60 students and wants to compare the significance of the pre-post differences (per critical thinking skill let’s say), why would they choose to do the comparison by performing z-tests with students’ percentages per skill before and after the intervention? Couldn’t they have just estimated the pre/post-means and run a t-test or a non parametric equivalent?
2. If they already had their z-tests for comparing separately whether the number (percentages) of students at each level of each skill has increased or decreased significantly, why would they continue with contigency tables and chi-square for checking whether students transition from skill-level to skill-level (low…high..etc) for each skill separeately, is significant or not? I mean do you think that this info really adds to their argument about the efficacy of their intervention regarding the target-skills?
Thank you very much.
Maria,
1. If you are trying to compare before and after data, the usual approach is to use a paired t-test of a paired Wilcoxon signed ranks test. Both are described on the website.
2. I don’t completely understand this question.
Charles
Thank you very much, Charles.
Let me clarify my 2nd question: if someone does find a significant gain in the learning outcomes of their interst by comparing pre-post data, is there actually a reason for them to search with chi-square whether the transition of students from “low to middle” or from “middle to high” level responses is significant too? Do you think that this info can really strengthen the argument about the efficacy of the intervention which was already shown, or it is practically useless?
Maria,
I don’t know what chi-square test you are referring to in the question “is there actually a reason for them to search with chi-square whether the transition of students from “low to middle” or from “middle to high” level responses is significant too?”
Charles
First of all, you are doing a really great job here. Thank you very much.
My question is: Can someone use Cronbach’s alpha in order to come up with conclusions about the reliability of a questionnare that includes only open-ended questions? These open-ended questions are supposed to elicit critical thinking skills from the respondents and they are coded per skill as “insufficient”, “low”, “middle” and “high”.
Maria,
You can use Cronbach’s alpha as long as you have an objective way to code the responses as “insufficient”, “low”, “middle” and “high”, and you can assign numeric values to these responses (e.g. as 0, 1, 2, 3).
Charles
Thank you very much for your prompt, clear answer.
Dear Sir,
Thanks for the further explanations. What if every student answered every question correctly? That’ll result in 11 for all cells M4-M15, correct? And therefore, the variance in the totals would be 0 (cell B21). How would you interpret such a result with respect to the alpha, please?
Thank you,
Marc
Marc,
If everyone answers the question correctly, in some sense the reliability would be perfect, i.e. 1, but not particularly interesting. For many of the reliability measurements, the mathematical result in extreme situation, such as this one, is counter-intuitive or not very helpful. Often because the variance is zero.
Charles
Charles,
Thank you very much indeed. That really helps my discussion and is a good contra argument
Marc
Hi Charles , I have a question here…
I am doing single subject. Questionnaire (Scale 1- 4) was administered 15 times with 3 subjects on 15 days which meant
1. 5 time baseline
2. 5 time intervention
3. 5 time withdrawn
My question here is how do I calculate cronbachs’ alpha with 15 time different phase?
Tiffany,
You would typically run Cronbach’s alpha multiple times, once per each of the time periods. This is of course impossible if you only have one subject (although you also say that you have three subjects).
Charles
Sir I need your help
Can’t you help me about kuder richard formula 20
I need exact explenation about kuder richard formula 20
thanks.
Sorry, but I don’t have anything else to add to what I responded earlier.
Charles
Hi there,
I have a very basic question. I am doing exploratory research with 500+ participants in predicting risk and thriving behaviours. My problem is that some of my outcome variables have only two items, thus my Cronbach alphas are always .50-.65 range. I’ve been reading that it is not even acceptable to run alpha analysis when you only have two items. Any thoughts for or against this practice?
There really isn’t much point in running Cronbach’s alpha with only two items, but you can calculate a result. Although I haven’t really thought it through, you might try using Cohen’s kappa to see whether there is agreement among the participants between the two items.
Charles
The variables are all continuous , and as I understand Cohen’s kappa is for inter-rater agreement on categorical variables.
Good point.
Charles
Hi,
For my thesis I have made two sections first is a multiple choice questionnaire and second is a 5 point likert scale. May I use split half method for the questionnaire and cronbach alpha for the rating scale? Please help.
You can use Cronbach’s alpha for the Likert scale. You can use either Cronbach’s alpha or split half for multiple choice questions.
Charles
Help pls! We have rows of necessities such as food, etc. and column of value like very important, important, etc. the total is always 50. And we have computed the alpha which resulted to -2.something. What does it interpret?
50 because 50 is our total respondents. This is a research our adviser told us to use cronbach but we dont know how to interpret it on our study. Our study is about minimum wage earners
Kim,
I am sorry, but I don’t completely understand the situation that you are describing. Are you saying that the alpha value is a negative value less than -2? This is a very unlikely result (sic).
Charles
Thank you for this Charles.
Can I please ask you to clarify my problem with a reliability test that I carried out pre and post survey. The cronbach’s alpha values were in the range of 0.73 to 0.90 for the pilot tests on 10 responses, deeming the scale to be reliable. However, when I ran a reliability test post survey with 82 responses, the cronbach’s alpha’s ranged from 0.57 to 0.83. The cronbach alpha values had decreased for some of the constructs and since as per the literature, constructs with values below 0.70 are said to have poor reliability, I am not sure what kind of inference I can make out of this situation for my research. Also , at this stage I cannot delete any items off the questionnaire because it is post survey. Can you please suggest an explanation for the constructs with lower alpha values and how I can defend their reliability for my research.
Unfortunately, a pilot test of 10 responses is not so much, and so it is entirely possible that the actual Cronbach’s alpha is different from what you found; in fact if you set the significance level to 95% (alpha = .05), you should assume that one out of 20 times you could get surprised in this way.
The .70 value is only a guideline. I have read others saying that .60 is also acceptable. This sort of problem happens. The only thing that I can suggest is to report your findings as they are. Clearly some of the alpha values are higher than .70, which is good. For the ones that are much lower, you can explain what you might do in the future differently.
Charles
Thank you for this Charles.
Your website has been most helpful.
Dear Charles,
Thanks for the crystal clear explanation, it was very helpful.
I have one question that I’ve been struggling with lately.
Suppose I have 6 items (i.e. questions), that 100 participants (i.e. cases) answered on a continuous scrolling bar yielding valued between -350 and 350. I’d like to know whether these 6 items are “internally consistent” so I proceed to computing Chronbach’s alpha. However, should I, or should I not mean-center the 6 responses of each subject before computing the alpha?
The reason of my question is this: I noticed that subjects have very consistent spatial biases in the way the use my scale, so I tried mean-centering the scores by subject. As a result, the magnitude of alpha was strongly decreased.
This seems to derive from the fact that mean-centering by subject decreases the “total variance” component of the alpha formula, more than it does the (sum of the) within-item variance. However, intuitively, I don’t understand why differences in the way subjects use the scale (independently of what items the scale represent) should affect a measure of its internal reliability.
Surely, I’m getting something wrong, though I don’t quite know what.
Any ideas?
Thanks!
gabe
Gabe,
It depends on what you mean by “mean centering”. If you calculate the mean for each question and then for each participant and each question you subtract the mean for that question from the score of that participant for that question, Cronbach’s alpha will be the same.
Charles
Hi,
I created and performed an attitudinal survey regarding how people believe that are being treated in a particular company. I am looking at factors correlated with and/or those that predict work-life balance. I have extracted a number of factors from the literature which are associated with work life satisfaction, and I have adapted questions accordingly. I have administered the survey and now am trying to make sure it is a reliable and valid indicator. I used your (awesome) tool and have a high Cronbach alpha (>.90). What type of test should I run for validity? It may be that I publish this, so I want to make sure I can at least comment on some psychometric properties. Is Cronbach enough and, if not, what would you recommend? I am not going for the most robust analysis in the world, just something that provides that this is a reasonably credible instrument. Thanks!
Dan
Dan,
Here is a response to a similar question that I found on another site. I hope that you find it useful.
Charles
Julia B. Smith · 41.59 · 90.86 · Oakland University
If this is too basic, I apologize, but…
Reliability examines whether you are getting consistent information. Validity examines whether the information you are getting measures what you think it measures. My basic example is a scale – I can get on the scale 15 times in a row, get the same information each time, and that is reliable. But if I want to use the scale to tell me how tall I am, that is not valid.
Consequently, using a statistical tool to examine validity is entirely anchored in what it is you think is being measured, and what other source of information you have to compare it to. If I have a survey that I think measures depression, I am going to want to compare the results on that survey to results on an instrument that is already known to measure depression. That statistical analysis would require correlation, but the basis of the validity argument rests on the other source of information (and what is known about it).
Recall that there are several types of validity (content validity, construct validity, outcome validity, etc.), and each requires a different kind of examination. I have attached an article that does a nice job of discussing the problem of testing validity applied to student evaluation of college instructors.
Onwuegbuzie_et_al2007.pdf
Hi,
Can i use cronbachs alpha for satisfaction questions on a scale 1 to 100, with 100 being the most satisfied?
Ben,
Yes, you can use Cronbach’s alpha in this cazse.
Charles
Dear Charles,
first of all: Thanks for this awesome website. It already helped a lot!
My question: I already made all the calculations to get to the point of Figure 3 (Example 2). Now I need to figure out, which of my items can be omitted. You wrote that the one with the lowest alpha value affects the result the most. So it’s better to remove items with the highest alpha values? In the next step the omission of one item changes the alpha value of the others, right? Does this influence order?
Thanks a lot!
Christian
Dear Christian,
I am pleased that you find the website helpful.
Which item to remove really depends on what your objective is. If you objective is to increase reliability then you would want to remove the one with the lowest alpha value.
Removal of one item will change the values of the others. I don’t know how it impacts the order, but I suspect that the order can change.
Charles
Dear Charles,
thank you for your response.
As I already have about 20 items and due to this a high alpha (~0,95) I want to remove several items.
That’s why I’m wondering, which items would be best to keep and which items I can remove from my list.
Christian
Excuse me Charles,
just to get things clear:
Would you, in my case, recommend to delete the items with the lowest alphas until I only have a few items (say about 5) left, but still have an acceptable overall alpha for the scale?
Christian
Christian,
It is hard for me to say since I don’t know your objective. If you would prefer an example with fewer questions, then I would probably choose the course of action that you have described, especially since your Cronbach’s Alpha is 95% (which is quite high), and so it seems that all the questions are pretty much testing the same thing.
Charles
Hello
require your assistance to calculate the Cronbach’s alpha for my questionnaire
it consists 4 Section and in each section there are a number of questions and the last section two open questions
it is measured as well
when I calculate the number of items
how I do it
I count the number of question or what
if you have an email I want to send the result for you please
regards
You can send an Excel spreadsheet with your data to my email address, which you can find at Contact Us.
Charles
Hi
My questionnaire was administered four times with 15 subjects on two days. How do I calculate cronbachs’ alpha? Should I take average of all four times for day 1 and day 2 and then average for the two days? Which values should I consider?
When you say that your “questionnaire was administered four times with 15 subjects on two days” does this mean
(1) that in total you have 15 subjects who answered the questionnaire, each subject answering the questionnaire one time, or
(2) as in (1) except that you had 15 subjects four times, and so you had 60 subjects in total answering the questionnaire, or
(3) 15 subjects answered the same questionnaire four times?
If the situation is (1) or (2), you can simply apply Cronbach’s alpha on all 15 (or 60) subjects, ignoring the day that they answered the questionnaire (unless you think that for some reason this is relevant).
If the situation is (3), then you should probably report four different Cronbach’s alpha values, one for each time the 15 subjects answered the questionnaire. I might give a different answer if I knew why they needed to answer the same questionnaire four times in two days.
Charles
They answered the same questionnaire four times on each of the two days. this was done to see any significant difference in subjective responses before and after a rest period.
so we had following experimental design:
day 1 (1) day 1 (2) day 1 (3) day 1 (4)
s1-s15 s1-s15 s1-s15 s1-s15
day 2 (1) day 2 (2) day 3 (3) day 4 (4)
s1-s15 s1-s15 s1-s15 s1-s15
You can use repeated measures ANOVA to determine whether there is a significant difference between the test results.
You can use Cronbach’s alpha to measure the reliability of the test, but in this case, I would calculate four separate Cronbach alphas.
Charles
Hi, I have problem with cronbach’s alpha. I only have 3 questions for one variable, in which the alpha is only 0.372. However, when I deleted one question, it is still low as 0.4978. Is it still possible to use the data for regression, while the alpha is only 0.4978? thanks
Dani,
I would think that you could still use regression in this case. But you should make sure that the model has a good fit.
Charles
hello !
I would like to do a Cronbach for my test but somehow i am not sure it is pertinent.
I’m not confident in doing this kind of work so i will explain detailfully.
Actually, there is a question and 7 possibilities of answer but only one is the good one.
So i wrote 1 if succeed, and 0 if didn’t succeed.
Then i did the cronbach test. 28 questions. 11 persons.
So it means (k/(k-1)) = 28/27 = 1,04. Isn’t it ?
Then i should calculate the variance for each question, one by one
(so it means if i get only 1 for all the answer, variance will be 0). Then i add them.
And then , this is where i have difficulties : i should calculate the variance between the total of the the 28 questions ? Or variance between each person ?
If i do it between each person i get -0,77
If i do it between the questions i get 0,46
And if i fake to have almost always good answer, i get 1,03 for example. Is it normal ?
Also I tried to do it question per question to find out which of the questions put the level so down. Is there a special formula for this ? Or should i apply it 28 times without one item.
Thank you so very much for your answer ! 🙂
Lilla,
I wasn’t able to follow all the steps you listed, but in any case you have the following options for computing Cronbach’s alpha
1. Use any of the techniques described on the referenced webpage
2. View the Excel worksheets that carry out the various techniques described on the referenced webpage. You can download these worksheets for free from the webpage Examples Workbooks.
3. Use the Real Statistics CRONALPHA function or the Cronbach’s Alpha option on the Real Statistics Reliability data analysis tool.
Charles
hi,
i want to test the reliability of a multiple choice test. how do i code the responses and how do i find the reliability using cronbach alpha
Natasha,
The simplest way to code the response is 1 for a correct answer and 0 for an incorrect answer. You can then calculate Cronbach’s alpha using any of the approaches described on the referenced webpage.
Charles
You are my lifesaver!
I have trouble with calculate cronbach alpha until I saw this page.
I finally got my cronbach alpha answer through Excel which is written by you.
Your posting is really helpful to me.
Thank you!
Good to hear that the information was helpful.
Charles
Can I find the reliability of a test using excel?
Kristine,
One approach may be to use Cronbach’s alpha as described on the referenced webpage.
Charles
Hi! I want to know the reliability of a 4o-item Math Test. How would I do that in SPSS? What data am I going to enter?
Kristine,
Sorry, but I am not familiar with SPSS. The Real Statistics Resource Pack provides such capabilities.
Charles
Dear Charles
This is a wonderful website.
Kindly assist I am administering a questionnaire in a census survey of 86 target respondents. The questionnaire has a total of 23 questions some of which have sub items. How many sample respondents should I use for calculating cronbach alpha in the pre-test?
Joseph
Joseph,
You can use the Statistical Power and Sample Size data analysis tool. Choose the Cronbach’s Alpha and Sample Size options.
Charles
Hi! How do you conduct cronbach alpha when the variables are income, consumption,a likert scale, and a dummy variable?
Justin,
Are using Cronbach’s alpha for a questionnaire? What do you mean by there are two variables? Do you mean two questions or two types of questions: those relating to income and those relating to consumption?
Charles
Yes, there are separate questions for income and consumption and we also have a question where it is answerable by 1 or 0 (dummy variable). We dont know how to do the cronbachs alpha for that dummy variable. 🙁
Justin,
Cronbach’s alpha can be used even when the questions take a value 1 (say for correct) and 0 (say for incorrect). This would cover True/False and multiple choice questions. The problem is that you can’t use Cronbach’s alpha with only one question. After all, Cronbach’s alpha measures internal consistency, but withonly one question there is no internal consistency to measure. The same is true for Kuder and Richardson.
Charles
Hi Charles,
I would like to know what kinds of questions could increase my Cronbach alpha? I did some readings to increase the quality of my questions in my questionnaire and after some piloting I have added 5 more items to the questionnaire but my alpha is still below 0.7 and I should delete some which are really critical questions. Do you have any suggestions? I feel so desperate.
Best,
Negar
Negar,
It is possible that your questionnaire is measuring more than one thing. In such cases, Cronbach’s alpha will be reduced. Instead of deleting questions, for the purposes of computing Cronbach’s alpha, you may need to split the questionnaire into two (or more) parts, one part for each group of questions that are measuring the same thing. In this way, you might be able to bring Cronbach’s alpha up to 0.7 on each part of the questionnaire.
If necessary, factor analysis can be used to figure out how to do the splitting of the questionnaire.
Charles
thnx for your help Charles
Hello Charles
I’m phd student and using questionnaire in my thesis .
I have 4 variable as independent and one dependent variable , each variable had 7-6 question. I tested Cronbach’s alpha for each variable in my pilot and remove and delete 3 to 4 question to increase my Cronbach’s alpha to .8 or .9 ,
and continue my data collection with 4-5 question for each variable.
now
i should analyses my main data with PLS,
but now, my Cronbach’s alpha decrease a gain and are less than .7 for each variable, and now i can not delete some question again.
what should i do now?
i really confuse.
thank
Nana
Is PLS partial least squares regression? Are the revised values for Cronbach’s alpha based on the latent variables (after applying PLS)?
If this is the situation, then I am not sure what the best approach is. If Cronbach’s alpha is just slightly less than .7 then I would worry about it too much.
Charles
thank you for your response. I have one more question. Can I do ANOVA by three schools? Is it possible to do ANOVA when you have ordinal data?
I don’t exactly know what you mean by doing ANOVA by three schools. You can do ANOVA with ordinal data, but I would not recommend it. You should use a non-parametric test instead (e.g. Kruskal-Wallis).
Charles
Excuse me sir. can I use average score of each teacher.
It depends on what you are measuring. If each student makes multiple evaluations of each teacher, you can use the average score (or total score) by each student of each teacher.
Charles
hello. I am writing from Mongolia. First of all, thanks for your help. I have been doing the survey that has 5 foint likert scale. the survey is Student satisfaction for teachers. my university has 3000 students and all students give answer to 130 teachers. How to calculate cronbach’s alpha?
Good to communicate with someone from Mongolia.
Enter the Likert scores in a range with 130 columns and 3000 rows and then either follow the approach from Example 4 or use Real Statistics’ CRONALPHA function or the Cronbach’s alpha option from the Reliability data analysis tool.
Charles
Thank you very much for answering my question.
Dear sir,
i had done a survey on questionnaire which contain 3 parts (A,B,C). I’m using cronbach alpha for my questionnaire. I had calculated those 3 parts and only part A and C are reliable, whereby the value part A ( 0.798), Part B ( 0.642) ,Part C (0.857). So what should I do with those result and are they reliable?
Adele,
The reliability ratings for Part A and C are quite good. Even Part B is not bad. The typical approach now is to see how Cronbach’s alpha changes by removing one question (as described on the referenced webpage). If say removing question Q4 from Part B increases the reliability for Part B to .7, then you should consider eliminating this question from Part B or changing it.
Charles
TQ sir for answering my question. I would like to remove the question but most of the score of all the questions in Part B are around 0.6. So should i remove all the questions?
Adele,
You probably don’t want to remove all the questions. You might want to think about changing the wording of all the questions a little. Alternatively, you can do nothing since .6 is a little on the low side, but acceptable to some.
Charles
Pls sir how did you calculate variances in row 17 and 21. will you mind using Figures from the table?
I really want to know this cronbach alpha
This is already explained in Figure 2 and the text between Figures 1 and 2. What else are you looking for?
Charles
does anyone know what the lower bound for the number of observations using the alpha is? i’ve heard it’s about ten times the number of items, however can’t be sure at all… many thanks!
Vince,
The Real Statistics Resource Pack provides a data analysis tool which calculates the sample size required for Cronbach’s alpha. See the following webpage for details:
https://real-statistics.com/reliability/cronbachs-alpha/cronbachs-alpha-continued/
Charles
I am research scholar. I need to know when to calculate Alpha. E.g For testing reliability, can I go with 10 sample units and the value of Alpha is 0.897. Would it be fine???
Give me reply somebody.
I don’t completely understand your question, but if you are using Cronbach’s alpha to test the reliability of a questionnaire based on 10 subjects, an alpha of .897 would generally indicate a high level of reliability.
Charles
Dear sir,
I want to use a test with high zero frequency in scoring , if the answer is rarely or sometimes or never then the score is equal zero (represent the same number) ?! so Cronbach’s alpha is low ?! but if I insert the data as, never represent=6 , rarely=5, sometimes=4,usually=3, often=2, always=1 then Cronbach’s alpha will increase !!
can I do that only to calculate Cronbach’s alpha ?! I mean changing the scoring only for the pilot study?!
Best,,
I just recalculated Example 4 on the referenced webpage using a Likert coding of 0 to 6 (instead of 1 to 7) by reducing each code by 1. The calculated value of Cronbach’s alpha did not change. Is this the sort of thing you are referring to?
Charles
Hi Charles,
I am so glad to find your website. Your demonstration of how to calculate Cronbach alpha is very relevant to my research. May I ask you one question?
I used a spelling test from a published study for my own research and I want to report the internal consistency reliability of this test based on the data I have collected. The spelling test examines how students spell four English vowel sounds. In such case, do I need to calculate Cronbach alpha for each target vowel sound? Is it appropriate to calculate Cronbach alpha for all items (all sounds) and report internal consistency reliability of the whole test?
Thank you so much for helping me.
If the test is for spelling of vowel sounds then one Cronbach’s alpha should be sufficient, but if you suspect there may be differences between vowels then I would compute separate Cronbach’s alphas for each vowel sound. I would do both and explain the results.
Charles
Thank you very much for answering my question.
Hi Charles,
Sorry I have one more question. I have four groups of participants (who have different characteristics) in my study and the same spelling test was administered to all groups. Do I need to calculate Cronbach’s alpha of the test for each group?
Thank you for helping me again.
I would do both. If the difference in the characteristics of the participants changes the reliability of the test, then this should become evident in the Cronbach’s alpha values.
Charles
Thank you!
Good day sir.
In my experiment survey of Y/N(1-0) questions, where all 3 questions got a perfect score of 1 from 15 respondents, I was not able to compute the alpha. The value of all the variances is 0.
The final result is k=3, eVar=0, var=0.
What could it mean?
Is it also possible to get a perfect score of 1 or 0 for the alpha? What would each result mean?
Thank you.
-K
K,
Unfortunately, in these circumstances Cronbach’s alpha is undefined because of division by zero. The good news is that all the respondents answered the same way, it is pretty easy to make evaluate the effectiveness of the survey even without using Cronbach’s alpha.
If on each of the three questions the subjects didn’t have identical scores, but if each subject got the same score on all three questions, then Cronbach’s alpha would be 1.
If you assign all scores of 0 or 1 at random, then Cronbach’s alpha is likely to be low (even negative).
Charles
Sir,
I want to know which input or inputs (out of 22) has more impact on output 1
which input/ inputs (out of 22) has more impact on output 2
which input/ inputs (out of 22) has more impact on output 3
which input/inputs (out of 22) has more impact on output 4
Raman,
Sorry, but the term “more impact” is unclear to me.
Charles
Hello Sir,
Firstly i want to say thanks for helping me to compute Cronbach’s alpha Value.
I go through almost all study material provided by you. But still in confusion which more statistical tools can be implement on my questionnaire data.
There are 22 input and 4 output.
I collected data for every input with respect to every output on likert scale
Q1 Rate the effect of Input 1 on Output 1
(Importance scale for every question)
(Extremely (Very Neither Imp (Very (Extremely
Important) Important) Nor UnImp. Unimportant) Unimportant)
1 2 3 4 5
Q2 Rate the effect of Input 1 on Output 2
Q3 Rate the effect of Input 1 on Output 3
Q4 Rate the effect of Input 1 on Output 4
Q5 Rate the effect of Input 2 on Output 1
Q6 Rate the effect of Input 2 on Output 2
Q7 Rate the effect of Input 2 on Output 3
Q8 Rate the effect of Input 2 on Output 4
Q9 Rate the effect of Input 3 on Output 1
………… and so on
Q85 Rate the effect of Input 22 on Output 1
Q86 Rate the effect of Input 22 on Output 2
Q 87 Rate the effect of Input 22 on Output 3
Q88 Rate the effect of Input 22 on Output 4
The no of respondent : 100
Thanking you in anticipation
Raman,
If I understand correctly, you have 88 questions using a Likert scale of 1 to 5 and 100 subjects. This is just like Example 4 of the referenced webpage but with 100 rows and 88 columns. You can use the CRONALPHA function or the Reliability data analysis tool to calculate Cronbach’s alpha.
Charles
Sir,
I have computed the value of Cronbach alpha.
But my query is now let me know which more tools such as Z test, correlaion, regression, factors could be used. The objective of my survey is to examine the impact of input factor in output.
Raman,
The phrase “examine the impact of input factor in output” is too vague. You need to create a hypothesis and then decide which test best tests this hypothesis.
Charles
Sir,
Thanks for replying
i want to know how many input parameters significantly influence output1; how many parameters significantly influence output2,parameters significantly influence output3, parameters significantly influence output4.
Raman,
What do you mean by “significantly influence”?
Charles
Hello,
Thank you for this very helpful site! I am curious about the use of Excel’s VarS function (instead of VarP). I notice you use VarP above, and I’m wondering why that is. If I understand Excel’s explanation, VarS would be used for a sample whereas VarP is used for a population. Wouldn’t most, if not all, of the scales we may develop require the formula for sample variance? Can you help me understand your choice to use VarP so that I can distinguish it’s use in my application of Cronbach’s Alpha for scales I am creating?
Thank you in advance,
Brenda
Brenda,
This is more of a mathematical issue. If you replace Var.P by Var.S throughout you will get the very same answer (since the n or n-1 terms in the denominator cancel out).
Charles
Oh yes, of course! Thank you!
Thanks Charles for ur kind reply. I want to check the influence of input parameres on the output parameters of a system. for this questionnaire study was performed.
the data collected table has 100 rows and 15 column.
I got the single value of Cronbach’s alpha. If there need to compute the value if Cronbach’s alpha for every column. If yes then how.. Kindly do needfull
Raman,
In the examples I have given on the referenced webpage, the columns correspond to “items” in a questionnaire (these are variables). Not only don’t you need to compute Cronbach’s alpha for each column, but such a calculation would yield an error since Cronbach’s alpha requires more than one item. On the website, however, Cronbach’s alpha on one column corresponds to Cronbach’s alpha on all the item leaving out that one column. This tells you the influence that specific item has on the entire questionnaire.
Charles
Thanks a lot
For example 1, can you explain why cells B20 and B21 do not have the same value? I’m trying to follow the formulas, but it seems like M17 in B20 would have the same value as the result of the formula for B21. Thank you!
Sammie,
B21 contains the variance of the row sums, i.e. VARP(M4:M15), while B20 contains the sum of the variances of the column sums, i.e. SUM(B17:L17). There is no reason why these should be equal.
Charles
Hi Charles,
My querry regarding Cronbach’s alpha values. No of respondand =100, The questionaire having 5 point scale ans consisit of 22 input and 4 output facors. I used the procedure expalined by you in figure 1. I got value. But some researcher are showing Cronbach’s alpha values for every input and output factors. If there need to compute the value if Cronbach’s alpha for for every input and output factors. If yes then how.. Kindly do needfull
Raman,
I don’t know what you mean by input and output factors in the context of Cronbach’s alpha.
Charles
Hi Charles,
I want to ask you about cronbach alpha.I have questionnaire which in this questionnaire have Likert type scale (1-4) and question yes/no.In questionnaire also have question like gender,marital status etc.How to get the cronbach alpha value using these data?Thank you
Hi Azili,
The idea of Cronbach’s alpha is to measure the internal consistency of the questionnaire. If the yes/no questions are measuring something different from the Likert questions (e.g. the yes/no questions are testing the subject’s knowledge and the Likert scale questions are determining their satisfaction) then there may be no point in calculating one Cronbach’s alpha; better to calculate two or more values.
If instead the yes/no questions are measuring something similar to the Likert questions then perhaps you can decide to treat the yes/no questions in a manner similar to the Likert scale questions. E.g. if the Likert scale questions measure satisfaction (with 0 very dissatisfied and 4 very satisfied) and yes = satisfied and no = not satisfied, then perhaps a coding like yes = 3 and no = 1 will work. In most cases, I suspect that the yes/no questions are measuring something different from the Likert scale questions and so you need to calculate multiple Cronbach alphas.
Charles
Hi Charles,
Hope you can help. We did a survey on identifying comparison in students’ attitude towards a list of 10 sub-factors (5 point Likert scale) on advantages of using a tool. The Cronbach alpha for each of the 2 colleges (A and B) with 2 columns (A and B) is over .9 which should reflect good reliability. My question is, if we then look into overall gender comparison analysis on students of the same two colleges using the same sub-factors with 2 columns (male and female), is it necessary to evaluate the Cronbach’s alpha for the gender comparison or can we assume that the reliability is the same?
Thanks in advance.
Kent,
If you suspect there is a gender bias to one of the questions, then I would evaluate Cronbach’s alpha for each gender. If one question seems to lower the score for one gender, then I would either reword or eliminate that question. If your goal is to compare the results by gender then you want to use a different test (e.g. t test, Mann-Whitney, etc.).
One other comment. The value you obtained for Cronbach’s alpha was high, but since it is over .9 it may be too high, meaning that the questions may be too similar and are just testing the same things.
Charles
Tqvm Charles for your response.
Yes, we do conduct the t-test for comparison. I wonder if it is necessary to provide Cronbach’s alpha value to indicate good reliability and internal consistency when we are using the same set of questions for college and gender comparisons. Is it a necessity to provide Cronbach’s alpha value to validate good reliability before doing a comparison between colleges or gender?
Thanks in advance.
Kent,
If you have gotten high values of Cronbach’s alpha in your test sample it is not necessary to repeat Cronbach’s alpha for new samples, unless you suspect there is something different about the new sample. As I stated in my previous response, if you suspect there is a gender bias, not in the responses per se, but in the internal consistency (perhaps because one question is misinterpreted by men or women), then you should repeat Cronbach’s alpha. In any case, since you will be testing the data anyway you probably should run CRonbach’s alpha just to make sure there is nothing strange going on.
Charles
Tqvm, Charles.
You have been a great help.
Take care.
I am trying to determine the reliability of an exam in which there are 25 multiple choice exams with a variable number of response choices (4, 5 or 10). Blank answers are given 1/4 credit. What is the most appropriate way to measure the exam reliability?
exams should have read questions
Mark,
The number of response choices shouldn’t really matter since each question is scored 1 for correct or 0 for incorrect. However things are more complicated with 1/4 credit for a blank answer. Perhaps one way to address this is to assign a score of 0 for incorrect, 4 for correct and 1 for blank and then use Cronbach’s alpha.
Charles
love the info. thanks so much.
so nice to have experts share their knowledge on the net.
what about sample size shoud be taken to test reliability having 20 questions with 7 piont scale likert type
Nasir,
To answer this question you need to spply additional information such as the expected/minimum value of Cronbach’s alpha, minimum power, etc.
Charles