The Matthew effect: Infant mortality in Canada and internationally

Objective. To examine whether the magnitude of improvement in the health st atus of a population over time is dependent on the previous health status o f that population. Design and Setting. A study of infant mortality rates in Canada's 12 provin ces and territories between the periods 1961-1965 and 1991-1995, and of inf ant mortality rates in 133 countries between 1960 and 1995. Main Outcome Measures. Spearman's rank correlations, relative risks, and ri sk differences to measure the relationship between infant mortality in the 1960s and changes in infant mortality between the 1960s and 1990s. Results. In Canada, regional rankings based on infant mortality rates in 19 61-1965 were strongly correlated (inversely) with rankings based on the per cent change in infant mortality between 1961-1965 and 1991-1995 (correlatio n coefficient = -.85). In contrast, internationally, rankings based on infa nt mortality rates in 133 countries in 1960 were positively correlated with percent change between 1960 and 1995 (correlation coefficient = .56). Regi onal differences in infant mortality rates, measured using relative risks, declined in Canada (highest relative risk: 4.2, compared with Ontario in th e 1960s; highest relative risk: 2.2, compared with Ontario in the 1990s) bu t increased globally (highest relative risk: 5.0, compared with industriali zed countries in 1960; highest relative risk: 15.1, compared with industria lized countries in 1995). Conclusions. Canadian regions with higher infant mortality rates in 1961-19 65 achieved larger improvements compared with regions with initially lower infant mortality rates. The pattern observed within Canada is unlike the pa ttern observed internationally.