Year of study Effect size 1989 1990–1999 2000 Grand total 1989 1990–1999 2000 Low 1 5 6 12 16.67% 41.67% 33.33% Medium 2 3 9 14 33.33% 25.00% 50.00% High 3 4 3 10 50.00% 33.33% 16.67% Grand total 6 12 18 36