Plotting the Bland-Altman limits of agreement

Plot a difference plot and limits of agreement.

1. Select a cell in the dataset.
2. On the Analyse-it ribbon tab, in the Statistical Analyses group, click Method Comparison(or Agreement depending on the edition), and then click Bland-Altman.
   The analysis task pane opens.
3. If the data are in 2 variables:
   1. In the X drop-down list, select the comparative or reference measurement procedure variable.
   2. In the Y drop-down list, select the test measurement procedure variable.
   Note: If the variables consist of replicate measurements, select the variable name that spans all the replicate columns.
4. If the data are in 2 variables with a separate variable identifying replicates of each item:
   1. In the X drop-down list, select the comparative or reference measurement procedure variable.
   2. In the Y drop-down list, select the test measurement procedure variable.
   3. In the Item drop-down list, select the variable identifying each item.
5. If the data are in a single variable with a separate variable matching each item and a variable identifying the method:
   1. In the Model drop-down menu, select Matched Pairs.
   2. In the Y drop-down list, select the measurement variable.
   3. In the Item drop-down list, select the item variable that identifies each item.
   4. In the Method drop-down list, select the method variable.
6. In the D drop-down list, select:

   Option	Description
   Difference	Plot the differences on the vertical axis.
   Relative Difference	Plot the differences relative to Z on the vertical axis.
   Ratio	Plot the ratio of the values on the vertical axis.

7. In the on Z drop-down list, select:

   Option	Description
   X	Plot X as a reference method on the horizontal axis.
   (X+Y)/2	Plot the average on the horizontal axis. Neither X or Y are reference methods.

8. In the Mean function drop-down list, select:

   Option	Description
   Constant	There is a constant relationship between D and Z.
   Linear function	There is a linear relationship between D and Z.

9. In the SD drop-down list, select:

   Option	Description
   Constant	The measurement error is constant throughout the measuring interval.
   Linear function	The measurement error is linear across the measuring interval.

10. Click Calculate.