6. Describing the relationship between two nominal variables

Myocardial infarction can be safely and effectively treated with aspirin, but how often aspirin is prescribed in actual medical practice is not well known. In particular, elderly patients are often at risk of not receiving aspirin when hospitalized for acute myocardial infarction. To address this issue, doctors conducted a study as part of the Cooperative Cardiovascular Project to determine how often aspirin is prescribed to elderly (65 years old) patients hospitalized for myocardial infarction. [Source: Krumholz, H.M., Radford, M.J., Ellerbeck, E.F., et al. (1995). Aspirin in the Treatment of Acute Myocardial Infarction in Elderly Medicare Beneficiaries.Circulation, 92, 2841-2847.]

Imagine that you conduct a similar study and find that among 10,027 patients 65 years of age or older, 5,770 patients received aspirin within the first 2 days of hospitalization. When grouped by age bracket, the study shows that aspirin was prescribed to 2,539 of 4,029 patients between 65 and 74 years of age, 2,135 of 3,923 patients between 75 and 84 years of age, and 1,096 of 2,075 patients 85 years of age or older.

Complete the following cross-classification table by entering a value in each of the 10 empty boxes.

Treatment
Age Group	Aspirin	No Aspirin	Total
65-74
75-84
85
Total	5,770		10,027

Refer to the following bar chart as you answer the questions that follow.

The bar chart shows the percentages for the age group and treatment data.

The percentages on the chart are computed by dividing each of the frequencies in a particular by the total for the .

The pattern in the graph suggests that for older patients hospitalized with myocardial infarction:

There may be a relationship between age and treatment; the likelihood of receiving aspirin treatment appears to be larger the older the patient

There may be a relationship between age and treatment; the likelihood of receiving aspirin treatment appears to be smaller the older the patient

There is no relationship between age and treatment