Sources of Error in the Production and Measurement of Standard Radiographs of the Foot

In procuring radiographs of the human foot for comparative purposes it was found that, by using the methods described, measurements of a chosen dimension (arch-height) on 36 films showed a standard deviation of ± 1·17 mm. In 10 contactcopies of a given radiograph the standard deviation of the measurements taken by two observers of this same dimension was ± 0·212 mm. It was not possible definitely to allocate the difference between these deviations to any particular source of variation. In the plantar view, measurements of angle between the axes of the first two metatarsals showed a standard deviation of ± 0·436 deg. (16 observations on contact-copies). In a series of 10 subjects each subjected to 10 different sets of circumstances under otherwise standard conditions, certain large alterations in the arch-height dimension were observed. Thus, flexing the weight-bearing knee in an otherwise standard position leads to a mean depression of the archheight of 3·9 mm. ± 0·933 mm. If in this position the trunk an...