Fleiss J L, Wallenstein S, Chilton N W, Goodson J M
Division of Biostatistics, Columbia University School of Public Health, New York, NY 10032.
J Clin Periodontol. 1988 Aug;15(7):411-4. doi: 10.1111/j.1600-051x.1988.tb01594.x.
Using a data set from the Forsyth Dental Center consisting of repeated measurements of periodontal attachment level on 22 patients over 1 year, we performed correlation analyses at 4 time points (baseline, 1 month, 6 months and 9 months) for 3 units of measurement (sites, teeth and quadrants). Values of the intraclass correlation coefficient were obtained for the cross-sectional measurements and for changes from baseline. The values were positive and often of appreciable magnitude, indicating that measurements of attachment level and of change in attachment level within the same mouth are positively correlated. Taking sites rather than patients as the units of statistical analysis in comparative clinical trials in periodontology will therefore tend to produce underestimated standard errors and overstated statistical significance.
利用福赛思牙科中心的一个数据集，该数据集包含22名患者在1年时间里牙周附着水平的重复测量值，我们在4个时间点（基线、1个月、6个月和9个月）对3种测量单位（位点、牙齿和象限）进行了相关性分析。获得了组内相关系数的值，用于横断面测量和相对于基线的变化。这些值为正，且往往幅度可观，表明同一张嘴内附着水平的测量值与附着水平变化值呈正相关。因此，在牙周病学的比较临床试验中，将位点而非患者作为统计分析单位往往会导致标准误差被低估，统计显著性被高估。
