Question

The following table describes hypothetical age-specific rates of heart disease in India and the United States in 2009. Also included are hypothetical age distributions for the two countries and the entire world population. Age Group (in years) % of Population in Age Group Heart Disease Rate per 100,000 person-years INDIA U.S.A. WORLD INDIA U.S.A. < 30 60% 30% 50% 50 75 30-55 30% 40% 30% 80 150 > 55 10% 30% 20% 120 400 • Calculate the crude rate of heart disease for each of the two countries. Suppose that you want to compare the rate of heart disease in India to that in the United States. You know that age is an important risk factor for heart disease. Examine the age distribution of each country’s population. • Should you use the two crude rates to compare the two countries? Why or why not? •

Answer 1

We are given the following distribution of age and heart disease rate for the two countries, and the world average.

Age Group (in years)	% of Population in Age Group			Heart Disease Rate per 100,000 person-years
	INDIA	U.S.A.	WORLD	INDIA	U.S.A.
< 30	60%	30%	50%	50	75
30-55	30%	40%	30%	80	150
> 55	10%	30%	20%	120	400

Based on this distribution, the crude rate of heart disease is obtained as the summation of % of population in each age group, times the heart disease rate in that age bracket. Hence,

The age distribution is quite the contrast in india as against U.S.A. The former has a much larger chunk of population in the less than 30 yrs bracket. The proportion of senior citizens in U.S.A. is double as against india, and half the proportion of youth as against India.

Just by taking a ratio of the crude rates, we may be inclined to conclude that the heart disease rate is about two and a half times in U.S.A. as against India. However, given that this risk increases with age, we should also account for the fact that India has a much higher proportion of youth. Hence, even though the overall rate is lesser, but if we adjust for the age distributions, it should become clear that the lower rate in India is not that low after all. The crude rates should definitely not be used to compare the two countries. While the situation is definitely worse in U.S.A. but the simple ratio of 162.5 to 66 does not represent an accurate picture either, of the age distribution of the Heart Disease Rates for the two countries.