Altitude and ischemic heart disease in tricultural New Mexico: an example of confounding

The relationship of male white ischemic heart disease (IHD) death rates to altitude falls to negligible levels when New Mexico populations are separated into Hispanic and Anglo. Low rates of IHD mortality characterize Hispanic males in New Mexico regardless of altitude. In comparison, New Mexico Anglo males have rates near the US average. The variable showing the most consistent positive relationship with altitude is per cent Hispanic. Mortimer et al. (N Engl J Med 296:581--587, 1977) reported a reduction in coronary heart disease mortality in New Mexico white males with an increase in altitude. The current authors claim that this is an example of confounding. They find that the relationship between IHD mortality and altitude is largely due to the intervening variable, per cent Hispanic. Ethnicity demands major attention in epidemiologic studies in tricultural New Mexico.