The researchers collected information on the numbers of revascularization procedures done in the year after cardiac catheterization. Then, they compared the frequency with which this procedure was performed in men versus women. The researchers did this by using three different levels of statistical adjustment to equalize factors that might influence the decision to offer treatment. First, they did not account for any patient factors. Next, they accounted for general factors, such as age and previous heart disease. Finally, they accounted for the severity of disease seen on catheterization.