
I just noticed something odd related to this that is making me wonder how CODAP treats missing values. I found a situation where the missing value seems to be treated as zero for making a particular calculation, but at other times the missing value is ignored for making the calculation. Look at the following three images and note especially the change in the intercept for the least squares line on the graph. At first, when a new case is added, it seems the % population and % cases for white people are being treated as zero, as the intercept changes from -23 to -16. Then, I added in some data (but not the data for % population and % cases for white people) and the intercept goes back to -23. So in the second image, it seems the missing data is being treated as zero, whereas in the third image, the missing data seems like it is being ignored.