Effect of recall on estimation of non-fatal injury rates: a community based study in Tanzania.

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.