Two-dimensional cephalometry is widely used for monitoring orthodontic treatments and for quantifying the outcome of maxillofacial surgery. Despite careful use of a cephalostat, successive radiographs might differ due to slight differences in patient posture. This study evaluates the reliability of lateral cephalometric measurements and estimates the impact of patient positioning on this reliability. We studied cephalograms of 104 patients; 31 of them had two radiographs because the first was deemed unsuitable for cephalometric analysis. Using AudaxCeph 3.0 (Audax, Ljubljana, Slovenia), two observers traced each cephalogram twice, one month apart. We evaluated intra- and interobserver agreement via Bland-Altman analysis, intraclass correlation coefficient (ICC), standard error of measurement, and smallest detectable difference (SDD). First, we studied the reliability of the hard tissue part of the Tweed-Merrifield analysis for 73 single cephalograms and for the better ones of patients with two exposures. Then, we studied 31 unsatisfactory cephalograms, and the ones recorded at improved patient posture. Although intraobserver bias was less than 0.5° or 0.3 mm, interobserver bias was significant for most measurements. Intraobserver reliability was high (ICC > 0.9), whereas interobserver reliability was good (ICC > 0.83) except for FMPA, FMIA and OP. Head rotations and inclinations had little impact on reliability (e.g., interobserver SDD decreased for 3 of 11 measurements). We conclude that averaging the positions of bilateral structures enables a reliable cephalometric analysis in spite of imprecise patient posture. Retaking cephalograms is ethically questionable in such cases.
Air displacement plethysmography (ADP) is a widespread technique for assessing global obesity in both health and disease. The reliability of ADP has been demonstrated by studies focused on duplicate trials. The present study was purported to evaluate learning effects on the reliability of body composition assessment using the BOD POD system, the sole commercially available ADP instrument. To this end, quadruplicate trials were performed on a group of 105 subjects (51 women and 54 men). We estimated measurement error from pairs of consecutive trials—(1,2), (2,3), and (3,4)—to test the hypothesis that early measurements are subject to larger errors. Indeed, statistical analysis revealed that measures of reliability inferred from the first two trials were inferior to those computed for the other pairs of contiguous trials: for percent body fat (%BF), the standard error of measurement (SEM) was 1.04% for pair (1,2), 0.71% for pair (2,3), and 0.66% for pair (3,4); the two-way random effects model intraclass correlation coefficient (ICC) was 0.991 for pair (1,2), and 0.996 for pairs (2,3) and (3,4). Our findings suggest that, at least for novice subjects, the first ADP test should be regarded as a practice trial. When the remaining trials were pooled together, the reliability indices of single ADP tests were the following: ICC = 0.996, SEM = 0.70%, and minimum detectable change (MDC) = 1.93% for %BF, and ICC = 0.999, SEM = 0.49 kg, and MDC = 1.35 kg for fat-free mass (FFM). Thus, the present study pleads for eliminating learning effects to further increase the reliability of ADP.
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