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.