Plotting a difference plot and estimating the average bias

Plot a difference plot and estimate the average bias (average difference) between the methods.

1. Select a cell in the dataset.
2. On the Analyse-it ribbon tab, in the Statistical Analyses group, click Method Comparison, and then click:

   Option	Description
   Mean difference	Estimate the average difference using the mean of the differences.
   Median difference	Estimate the average difference using the median of the differences. Useful when the distribution of the differences is not normally distributed

   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	The differences are not related to magnitude.
   Relative Difference	The differences are related to magnitude.

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

   Option	Description
   X	X is a reference method.
   (X+Y)/2	Neither X or Y are reference methods.

8. Click Calculate.