PT  - JOURNAL ARTICLE
AU  - Schmidt, Wolf-Peter
AU  - Boisson, Sophie
AU  - Genser, Bernd
AU  - Barreto, Mauricio L
AU  - Baisley, Kathy
AU  - Filteau, Suzanne
AU  - Cairncross, Sandy
TI  - Weight-for-age z-score as a proxy marker for diarrhoea in epidemiological studies
AID  - 10.1136/jech.2009.099721
DP  - 2010 Dec 01
TA  - Journal of Epidemiology and Community Health
PG  - 1074--1079
VI  - 64
IP  - 12
4099  - http://jech.bmj.com/content/64/12/1074.short
4100  - http://jech.bmj.com/content/64/12/1074.full
SO  - J Epidemiol Community Health2010 Dec 01; 64
AB  - Background 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.Methods 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.Results 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.Conclusion Repeated WAZ measures appear to be a suitable proxy marker for diarrhoea in children, but have disadvantages in terms of specificity and study power.