Chinn S, Rona R J
Department of Community Medicine, United Medical School of Guy's Hospital, London.
J R Soc Med. 1987 Sep;80(9):544-6. doi: 10.1177/014107688708000904.
The National Study of Health and Growth (NSHG) is a surveillance system which monitors the growth of primary school children in England and Scotland, set up in 1972 following changes in the school milk and welfare system. However, the study contained few children from inner city areas or ethnic minorities. In 1982 its design was changed from one in which the same areas were surveyed every year, to two separate systems with areas surveyed every two years, one set of areas corresponding to those in the original study, and the other set consisting of inner city and ethnic minority areas. The precision of the estimates of trends in height and weight for each system was smaller than that of the original system, but by less than 50%, so that an overall gain in information was achieved. Studies of mixed longitudinal design are shown also to be generally, but not always, less efficient for estimating trends than independent cross-sectional surveys obtaining the same number of measurements.
全国健康与成长研究（NSHG）是一个监测英格兰和苏格兰小学生成长情况的监测系统，它于1972年随着学校牛奶和福利制度的变化而设立。然而，该研究涵盖的来自市中心地区或少数民族的儿童很少。1982年，其设计从每年对相同地区进行调查改为两个独立的系统，每两年对地区进行一次调查，一组地区与原研究中的地区相对应，另一组地区由市中心和少数民族地区组成。每个系统身高和体重趋势估计的精度低于原系统，但降低幅度不到50%，因此总体上实现了信息增益。混合纵向设计的研究还表明，与获得相同测量次数的独立横断面调查相比，在估计趋势方面通常（但并非总是）效率较低。
