Question

What does it generally mean when you have a RR=1, RR<1or a RR>1 • If you are confused look at the hormone replacement therapy abstracts. What did Grodstein et al. conclude and was their RR equal to, less than or greater than 1? What did the Women’s Health Initiative (WHI) study find? What did their respective RR represent? (We will cover these studies on 9/17 and 9/19 but the RR is from the epidemiology section) Who is the unit of analysis in ecological studies and what is the ecological fallacy?

Answer 1

RR stands for relative risk. It is thr ratio of risk of events of exposed group and control group. Its values can be:

• RR=1 it means that the risk of an occurrence is equal in both the exposed and control groups
• RR<1 = It means that the risk of occurrence is less in the control sample
• RR>1 = Implies that the risk is greater in the exposed group

Grodtsein et al concluded that the use of hormone after menopause appears to decrease risk for major coronary events in women without previously diagnosed coronary disease. The RR was 0.54 which was less than 1. This means that the relative risk in these women is less than the control group.

The following were the relative risks for different events according to the WHI:

• Heart attacks: 1.29
• Strokes : 1.41
• Breast cancer: 1.26
• Thromboembolic events : 2.1
• Colon cancer : 0.66
• Hip fractures : 0.63

The unit of analysis in an ecological study is a population.

Ecological fallacy is when we fail to analyse the data about an individual correctly because it has been inferred from a group that he or she is a part of.