Epidemiological methods in diarrhoea studies—an update

Background Diarrhoea remains a leading cause of morbidity and mortality but is
difficult to measure in epidemiological studies. Challenges include
the diagnosis based on self-reported symptoms, the logistical
burden of intensive surveillance and the variability of diarrhoea
in space, time and person.

Methods We review current practices in sampling procedures to measure
diarrhoea, and provide guidance for diarrhoea measurement
across a range of study goals. Using 14 available data sets, we
estimated typical design effects for clustering at household and village/neighbourhood
level, and measured the impact of adjusting for
baseline variables on the precision of intervention effect estimates.

Conclusions Using appropriate sampling strategies and outcome measures can
improve the efficiency, validity and comparability of diarrhoea studies.
Allocating large clusters in cluster randomized trials is compromized
by unpredictable design effects and should be carried out
only if the research question requires it.