请教各位，下述表述中的样本量是怎么算出的？ Sample size calculations were based on pilot data of mean changes in the incremental area under the curve (iAUC) for glucose and insulin (10% for glucose, 60% for insulin), estimates of population variability (SD 1% for glucose, 30% for insulin), and assuming a correlation coefficient of 0.5 between repeated measures of the outcomes. We estimated that 19 paired observations were needed to achieve a power of 0.90 to detect the smallest expected effect size in the primary outcome variables between the three interventions, while adopting a two-tailed testing and a 0.05 probability level.