Chinn S, Rona R J
Department of Public Health Medicine, United Medical School, Guy's Hospital, London.
Thorax. 1992 Sep;47(9):707-14. doi: 10.1136/thx.47.9.707.
No standard exists for the adjustment of lung function for height and age in children. Multiple regression should not be used on untransformed data because, for example, forced expiratory volume (FEV1), though normally distributed for height, age, and sex, has increasing standard deviation. A solution to the conflict is proposed.
Spirometry on representative samples of children aged 6.5 to 11.99 years in primary schools in England. After exclusion of children who did not provide two repeatable blows 910 white English boys and 722 girls had data on FEV1 and height. Means and standard deviations of FEV1 divided by height were plotted to determine whether logarithmic transformation of FEV1 was appropriate. Multiple regression was used to give predicted FEV1 for height and age on the transformed scale; back transformation gave predicted values in litres. Other lung function measures were analysed, and data on inner city children, children from ethnic minority groups, and Scottish children were described.
After logarithmic (ln) transformation of FEV1 standard deviation was constant. The ratios of actual and predicted values of FEV1 were normally distributed in boys and girls. From the means and standard deviations of these distributions, and the predicted values, centiles and standard deviation scores can be calculated.
The method described is valid because the assumption of stable variance for multiple regression was satisfied on the log scale and the variation of ratios of actual to predicted values on the original scale was well described by a normal distribution. The adoption of the method will lead to uniformity and greater ease of comparison of research findings.
儿童肺功能随身高和年龄的调整尚无标准。对于未转换的数据不应使用多元回归，因为例如用力呼气量（FEV1），尽管在身高、年龄和性别方面呈正态分布，但其标准差在增大。本文提出了一个解决这一矛盾的方法。
对英格兰小学6.5至11.99岁儿童的代表性样本进行肺功能测定。在排除未提供两次可重复吹气的儿童后，910名英国白人男孩和722名女孩有FEV1和身高的数据。绘制FEV1除以身高的均值和标准差，以确定FEV1的对数转换是否合适。使用多元回归在转换后的尺度上给出身高和年龄的预测FEV1；逆转换得到以升为单位的预测值。分析了其他肺功能指标，并描述了内城儿童、少数民族儿童和苏格兰儿童的数据。
FEV1经对数（ln）转换后标准差恒定。FEV1实际值与预测值的比值在男孩和女孩中呈正态分布。根据这些分布的均值、标准差以及预测值，可以计算百分位数和标准差分数。
所描述的方法是有效的，因为在对数尺度上满足了多元回归方差稳定的假设，并且原始尺度上实际值与预测值比值的变化可用正态分布很好地描述。采用该方法将导致研究结果的一致性和更易于比较。
