Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, WC1E 7HT London, UK.
J Epidemiol Community Health. 2010 Dec;64(12):1074-9. doi: 10.1136/jech.2009.099721. Epub 2009 Dec 1.
The validity of unblinded randomised trials testing interventions against diarrhoea is severely compromised by the potential for bias. Objective proxy markers for diarrhoea not relying on self-report are needed to assess the effect of interventions that cannot be blinded. Short-term changes in weight-for-age z-score (WAZ) may (due to catch-up growth) not be a clinically important marker for nutritional status. However, even a transient decrease in WAZ could indicate recent diarrhoea, and be interpreted as the effect of an intervention.
Using data from two large vitamin A trials from Ghana and Brazil, the immediate effect of the cumulative diarrhoea occurrence over 14 and 28 day time windows on WAZ was explored.
A very strong linear association was found between the number of days with diarrhoea over the last 14-28 days and WAZ. In both trials, differences in diarrhoea between the trial arms were associated with corresponding differences in WAZ.
Repeated WAZ measures appear to be a suitable proxy marker for diarrhoea in children, but have disadvantages in terms of specificity and study power.
非盲随机试验测试腹泻干预措施的有效性严重受到偏倚的影响。需要不依赖自我报告的客观代理标志物来评估无法进行盲法的干预措施的效果。体重与年龄的短期变化 z 分数（WAZ）可能（由于追赶性生长）不是营养状况的临床重要标志物。然而，即使 WAZ 短暂下降也可能表明最近发生了腹泻，并被解释为干预措施的效果。
利用来自加纳和巴西的两项大型维生素 A 试验的数据，探讨了在过去 14 天和 28 天时间窗口内累积腹泻发生天数对 WAZ 的即时影响。
在过去 14-28 天内腹泻天数与 WAZ 之间发现了非常强的线性关联。在两项试验中，试验组之间的腹泻差异与 WAZ 的相应差异相关。
反复测量 WAZ 似乎是儿童腹泻的一种合适的代理标志物，但在特异性和研究能力方面存在劣势。
