Facial measurements in clinical genetics: How important are the instruments we use?

Abstract

Prompted by our finding that a popular compendium of clinical measurements often suggests a transparent ruler as a suitable substitute for anthropometric calipers (which were typically used by the original researchers to collect the normative data), we compared facial measurements taken with a ruler and calipers. Our objectives were to compare facial measurement data taken with these instruments by two classes of observer: expert and inexperienced. Ten facial measurements were repeated on four medically normal women by one expert and one inexperienced observer. Both observers' data showed that the caliper-derived means were usually the larger, but, whereas the expert observer's caliper-derived data typically were the least variable, the novice observer had smaller standard deviations and ranges for the ruler-derived data. Statistically significant differences were found between the ruler- and caliper-derived data from both observers on all four subjects, except for subnasale-pogonion and stomion-pogonion. For the novice observer only, endocanthion-endocanthion, left exocanthion-endocanthion, and alare-alare were also nonsignificant. The calibrations of the sliding caliper and ruler were compared to determine if differences between them could explain the statistical results, but were the same. We concluded that the differences between the caliper- and ruler-derived measurements resulted because the ruler often could not be placed directly on the landmarks, as could the arms of the calipers. We recommend that clinicians interested in taking facial measurements to assess their patients consult the original publications for information on the techniques and instruments used so that reliable comparisons with the normative data can be made.