Question

Case Study

The following table shows the number of colon cancer deaths and person-years of risk by the frequency of aspirin for males and females.

Table 1. Rates of death from colon cancer, according to frequency of aspirin use in the cohort before patients with illness at enrollment were excluded.

		Aspirin Use (times per month)
		0	<1	1-15	>16
Men	Number of Deaths	378	184	127	85
	Person-years at risk	646,346	486,620	389,083	201,636
	Death rate per 100,000
	Rate ratio	1.00
Women	Number of Deaths	284	157	100	73
	Person-years at risk	705,064	671,927	505,854	265,424
	Death rate per 100,000
	Rate ratio	1.00

1. Calculate the death rates and the rate ratios for each of the aspirin-use categories in the above table.
2. Given the results in this table, what is your conclusion about the association between the use of aspirin and fatal colon cancer?

Answer 1

		Asprin	use	(times per	month)
		0	<1	1 - 15	>16
Men	Number of deaths	378	184	127	85
	Person-year at risk	646,346	486,620	389,083	201,636
	Death per 100,000	58.48	37.81	32.64	42.16
	Death rate per 100,000	0.05848%	0.03781%	0.03264%	0.04216%
Women	Number of deaths	284	157	100	73
	Person-year at risk	705,064	671,927	505,854	265,424
	Death per 100,000	40.28	23.37	19.77	27.5031
	Death rate per 100,000	0.04028%	0.02337%	0.01977%	0.02750%

Death rate per 100,000 is = $\frac{number of death*100,000}{person-year at risk}$