Fig. 2

Item-Person map representing all simulation data. Person abilities (left of centre line) are mapped against item difficulty (right of centre line). Students' ability is arranged from highest performing to lowest performing, and item difficulty is from most difficult to least difficult. Each '#' represents 5 participants. Each '.' represents 1 to 4 participants. The mean student ability ('M' on left of centre line) closely matches the mean of item difficulty ('M' on right of centre line). S = 1 standard deviation, T = 2 standard deviations