Figure 2

The estimated true ability of candidates taking the examination at each diet. The solid points are the estimates from the regression (s _d ). The thick black line is a fitted lowess line (locally weighted regression), and the thin black lines show lowess lines through the one standard error confidence intervals for the points. The thick dashed line is the 'dog-leg' curve (see text). The vertical dashed line indicates the date when unlimited attempts were allowed in the Part 1 examination.