The corrected atd angle.

The 'corrected' atd angle has been studied in 1,000 healthy subjects, and a normal range established. This corrected angle eliminates the huge errors due to lateral deviation of the triradius, and taking the print with the fingers adducted eliminates another major error. The corrected atd angle, although an improvement on an ordinary atd angle, is still affected by age, and studies will have to continue to subdivide subjects into discrete age groups. The distribution of the corrected atd angle is not normal, and the mean atd angle has limitations. Comparisons between groups of subjects are probably best made by making arbitrary limits for the range of normality, and some figures for these limits are suggested.