The Matthew effect: infant mortality in Canada and internationally.

OBJECTIVE: To examine whether the magnitude of improvement in the health status of a population over time is dependent on the previous health status of that population. DESIGN AND
SETTING: A study of infant mortality rates in Canada's 12 provinces and territories between the periods 1961-1965 and 1991-1995, and of infant mortality rates in 133 countries between 1960 and 1995. MAIN OUTCOME MEASURES: Spearman's rank correlations, relative risks, and risk 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 1961-1965 were strongly correlated (inversely) with rankings based on the percent change in infant mortality between 1961-1965 and 1991-1995 (correlation coefficient = -.85). In contrast, internationally, rankings based on infant mortality rates in 133 countries in 1960 were positively correlated with percent change between 1960 and 1995 (correlation coefficient =.56). Regional differences in infant mortality rates, measured using relative risks, declined in Canada (highest relative risk: 4.2, compared with Ontario in the 1960s; highest relative risk: 2.2, compared with Ontario in the 1990s) but increased globally (highest relative risk: 5.0, compared with industrialized countries in 1960; highest relative risk: 15.1, compared with industrialized countries in 1995).
CONCLUSIONS: Canadian regions with higher infant mortality rates in 1961-1965 achieved larger improvements compared with regions with initially lower infant mortality rates. The pattern observed within Canada is unlike the pattern observed internationally.