Study objective: To investigate the effect of recall on estimation of non-fatal injury rates in Tanzania.
Design: Retrospective population based survey.
Setting: Eight branches in an urban area and six villages in a relatively prosperous rural area in Tanzania.
Subjects: Individuals of all ages living in households selected by cluster sampling.
Main outcome measures: Estimated non-fatal injury rates calculated at each of the 12 recall periods (one
to 12 months before the interview).
Results: Out of a population of 15 223 persons, 509 individuals reported 516 injuries during the
preceding year. Of these 313 (61.5%) were males and 196 (38.5%) females. The data showed notable
declining incidence rates from 72 per 1000 person-years when based on a one month recall period to
32.7 per 1000 person-years for a 12 month recall period (55% decline). The decline was found for injuries
resulting in fewer than 30 days of disability whereas rates for severe injuries (disability of 30 days or
more) did not show a consistent variation with recall period. Decline in injury rates by recall period was
higher in rural than in urban areas. Age, sex, and education did not notably affect recall.
Conclusions: Longer recall periods underestimate injury rates compared with shorter recall periods. For
severe injuries, a recall period of up to 12 months does not affect the rate estimates. It is essential that a
recall period of less than three months be used to calculate injury rates for less severe injuries.