An application of hierarchical linear models to meta-analysis in nursing research

OBJECTIVES: To compare the effect of using regions of interest (ROIs) of different size and shape on the fractal index of alveolar bone. STUDY DESIGN: Two sets of clinical posterior bitewing radiographs were used to calculate the fractal index (S). Two comparisons were made. First, S was calculated from large interdental ROIs that included small amounts of root structure and compared with S from small ROIs that included no root structures. Then S was calculated from large interdental ROIs (similar to those used for the first set) and compared with S calculated from ROIs that included nearly all of the mandibular alveolar bone (and adjacent root) present on the bitewing. RESULTS: For the first comparison, paired t-tests showed that fractal indices calculated with the large ROIs were significantly different from the respective indices calculated from the small ROIs (P < 0.001). For the second comparison, the fractal indices calculated from the large quadrant ROIs were not significantly different from those calculated from the large ROIs (P = 0.120). CONCLUSION: ROI size and shape may affect the results of fractal analysis of alveolar bone.