This illustrates the result of selection against small gall size. The trend in the mean would be in the opposite direction if the selection was against large gall size, while the trends in the variances would be similar.
|Entire sample of galls||Mean = 18.71 mm
Variance = 9.70
|After 50% of galls < 16 mm are parasitized||Mean = 19.20 mm
Variance = 7.68
|After 100% of galls < 16 mm are parasitized||Mean = 19.82 mm
Variance = 5.44