前后测量设计资料中个体生长问题.docVIP

前后测量设计资料中个体生长问题 　【关键词】 前后测量 Problem of the individual change in pretestposttest design 　　【Abstract】 AIM: To study the individual change over time in pretestposttest design. METHODS: Using the banting of obese children as an example, there were 2 groups: one is the treatment group with the obese children receiving drug to control weight, the other is the control group with the children of standard weight. At the age of 8 and 10, the weight was measured. The hypothesized mean of each group children weight was Y1(t1)=31.0, Y0(t1)=23.0， Y1(t2)=36.0， Y0(t2)=28.0. In the absence of treatment, the hypothesized mean Y1*(t2) was 41.0. RESULTS: Using simple gain scores to estimate the treatment effect, α=36.0-31.0-(28.0-23.0)=0 (kg), this indicated that after experiment the 2 groups were not different in children weight, and the treatment effect didnt exist. But the true treatment effect was Y1(t2)-Y1*(t2)=36.0-41.0=-5.0(kg), which showed that the treatment effect existed and the children weight was different after treatment. CONCLUSION: The 4 kinds of individual changing trends in pretestposttest design show the problem of the individual change cant be ignored when we analyze the data of pretestposttest design. 　　【Keywords】 pretestposttest design；individual change 　　【摘要】 目的：探讨前后测量设计资料中伴随的个体自然生长现象. 方法：以肥胖儿童的减肥试验为例，假设有两组儿童，一组为处理组，该组儿童为肥胖儿童组接受减肥药物控制体质量；另一组为对照组，该组儿童为标准体质量儿童组，分别在8岁和10岁时测量儿童的体质量，假设两组儿童在试验前后体质量的均值分别为Y1(t1)=31.0， Y0(t1)=23.0， Y1(t2)=36.0， Y0(t2)=28.0,在处理组缺失干预时Y1*(t2)=41.0. 结果：用简单得分法估计处理效应， α=36.0-31.0-(28.0-23.0)=0(kg)，说明两组儿童试验后的体质量无差异，处理效应不存在，但是真实的处理效应为Y1(t2)-Y1*(t2)=36.0-41.0=-5.0(kg)，说明处理效应是存在的，即施加干预前后儿童的体质量有差别. 结论：总结了前后测量设计资料个体生长趋势的4种情况，提示我们在分析前后测量设计资料时个体自然生长问题不容忽视. 　　【关键词】 前后测量；个体生长 　　0引言 　　前后测量试验设计（pretestposttest design）方法是医学科研设计中普遍采用的一种试验设计方法，因为这种设计方法考虑了各组试验前（基础值）的差别，并且试验前数据提供了更多个体差别的额外信息，降低了误差方差，提高了检验效能［1-2］. 但是这其中还有一个“隐藏问题”容易被忽视，即个体随时间的自然生长问题. 自然生长问题是生物界的规律，是不可避免的，医学试验的受试对象一般是动物个体或者人体，所以这一问题就必须要考虑. 例如，在治疗高血压的自身前后对照临床试验中，对大多数成人来说，血压会随着年龄而增加，因此就存在一个潜在的“生长”