Limits of Agreement

On this webpage, we provide additional information about how to create a Bland-Alman Plot using Excel charting capabilities.

Example

Note that the x values for the scatter plot in Figure 2 of Bland-Altman Plot range from 30 to 80, and so we specify in range V2:Y3 of Figure 1 (which is a repeat of Figure 4 of Bland-Altman Plot) the endpoints for the three horizontal lines (for the mean and lower and upper limits) shown in Figure 2.

Bland Altman agreement levels

Figure 1 – Calculation of Mean and Limits of Agreement

We add these horizontal lines to the scatter diagram by adding three series to the scatter diagram data.

Adding the horizontal lines

To do this, click on the scatter diagram and then select Design > Data|Select Data. This brings up a dialog box as shown in Figure 2.

Dialog-box-horizontal-lines

Figure 2 – Adding the Horizontal Lines

Initially, only the first series was present. We have added three series corresponding to the three horizontal lines. We now show how to add the lower limit series (the procedure to add the mean and upper limit series is similar).

Click on the Add button on the left-hand side of the dialog box in Figure 3. Fill in the values indicated (referring to the cells in Figure 1) on the dialog box that appears as shown in Figure 3, and click on the OK button.

Adding lower limits

Figure 3 – Adding the Lower Limit series

Filling in the horizontal lines

Actually, this won’t add the horizontal line, but only the two endpoints of this line. To add the line, we need to right-click on either of these endpoints (on the chart shown in Figure 1 of Bland-Altman Plot) and then choose the Change Series Chart Type … option from the menu that appears. This brings up the dialog box shown in Figure 4.

Dialog change chart type

Figure 4 – Change Chart Type dialog box

Now click on the downward-pointing arrow next to the “lower” series and change the Chart Type from Scatter to Scatter with Straight Line and then click on the OK button.

Examples Workbook

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

Reference

Giavarina, D. (2015) Understanding Bland-Altman. Biochemia Medica
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4470095/

Bansel, S. (2019) How to create combination charts in Excel – step-by-step tutorial.
https://trumpexcel.com/combination-charts-in-excel/

8 thoughts on “Limits of Agreement”

  2. Dear Charles,

    Thank you so much for this explanation. I am currently using the non-parametric Blandt and Altman method, because of violation of normal data distribution of the differences. Therefore, the average bias is estimated as the median of the differences. But, how should I best calculate the 2.5th and 97.5th percentiles score i.e. limits of agreement for a non-parametric Blandt and Altman?

    I have currently calculated the percentiles for each difference according to the following instructions . But it does not provide the means to calculate the values for the 2.5th and 97.5th percentiles. http://advisor.morningstar.com/Enterprise/VTC/Morningstar_Ranks_Absolute_Percentile_Fractional.pdf. Is that an appropriate method for any percentile? If so, what is the best way to estimate the value for the 2.5th and 97.5th percentile? Is there any tutorial available on this topic?
    Thank you for your advice.

    Reply

      • total allowable error (TEa).”Bias can be compared against a systematic error%, and imprecision against a random error%, of a total allowable error goal. The total allowable error can be specified in absolute units of the analyte, as a percentage of analyte concentration, or as a combination of the two in which case the larger of the absolute and percentage concentration is used.” tooken from analyse-it.com

        Reply

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