This paper describes how the methodology used for measuring diarrhoeal
morbidity has changed over time and assesses how differences in episode
definition have affected estimates of diarrhoeal morbidity among
children aged less than five years. The episode definition used in 73
studies included in three previously-published literature reviews was
identified. In earlier work, a method was developed that adjusts
morbidity estimates to take account of differences in episode
definition. This adjustment method was applied to the studies
identified in these three literature reviews. Episode definitions were
better documented and were more consistent in studies published after
1980. Adjusting morbidity estimates to account for definitional
differences did not substantially alter the reviews\u2019 conclusions.
Diarrhoeal surveillance has steadily improved since 1980, with
methodology becoming more consistent between studies and better
documented. Although episode definitions have changed over time, the
morbidity estimates derived in the three reviews appear robust to these
changes