Figure 2. Difference between non-cycloplegic autorefraction obtained at the 15-year ALSPAC research clinic and subjective refraction recorded by the subject’s own optometrist. Two frequency distributions are plotted according to whether the Avon Longitudinal Study of Parents and Children (ALSPAC) clinic record indicated that the subject was or was not wearing contact lenses during the autorefraction test. Note the reduction in outliers and better conformity to a normal distribution when contact lens wear was excluded.