- Demonstrate respectful, constructive, adaptive interactions with peers and/or facilitators, including punctual attendance, advanced preparation, professionalism, and giving and receiving feedback
- Interpret and calculate statistical tests that are used in the health sciences
In the large-group session, you learned about a few basic statistical methods used in the health sciences. In this small group session, you will calculate some statistical tests to better understand how to interpret them when reading the literature.
Odds ratio
The odds ratio is the measure of association for a case-control study. It quantifies the relationship between exposure (such as eating food or attending an event) and a disease in a case-control study. The odds ratio is calculated using the number of case patients who did or did not have exposure to a factor (such as a particular food) and the number of controls who did or did not have the exposure. The odds ratio tells us how much higher the odds of exposure are among case patients than among controls.
Risk ratio
A risk ratio (RR), also called relative risk, compares the risk of a health event (disease, injury, risk factor, or death) among one group with the risk among another group. It does so by dividing the risk (incidence proportion, attack rate) in group 1 by the risk (incidence proportion, attack rate) in group 2. The two groups are typically differentiated by such demographic factors as sex (e.g., males versus females) or by exposure to a suspected risk factor (e.g., did or did not eat potato salad). Often, the group of primary interest is labeled the exposed group, and the comparison group is labeled the unexposed group.
Risk Ratios are typically used in cohort studies.
It is best to solve the following problems as a group.
- Go to the board to figure this out.
- Do not use any online calculators.
- Show your work!
- Discuss what the numbers mean.
Problem 1
A case-control study assesses the relationship between sleep satisfaction and breast cancer. A total of 2852 subjects are enrolled in the study. Half of the study participants have breast cancer, and half are matched controls. The investigators report that 276 of the patients with breast cancer and 215 of the controls were dissatisfied with their sleep satisfaction.
Based on these results, what is the best estimate of the odds ratio for breast cancer among those who were satisfied with their sleep versus those who were dissatisfied with their sleep satisfaction?
Problem 2
A cohort study in smokers assesses the role of the SNP rs1051730 and the risk of developing lung cancer. One hundred thirty smokers are followed for ten years to assess the development of myocardial infarction. Ten develop lung cancer in the group of 60 patients with “normal” SNP rs1051730. In the group of 70 patients with an SNP rs1051730 variant, 25 develop lung cancer.
Which of the following is the best estimate of relative risk in patients with a variant in the SNP rs1051730 compared to patients with a normal genotype of SNP rs1051730?
Problem 3
When reading a recent case-control investigation, you viewed the following statement: "Daily cannabis use was associated with increased odds of psychotic disorder compared with never users (adjusted odds ratio [OR] 3.2, 95% CI 2.2–4.1), increasing to nearly five-times increased odds for daily use of high-potency types of cannabis (4.8, 2.5–6.3).
Using the term “percentage,” what is another possible way of interpreting this finding regarding the use of high-potency cannabis?
Problem 4
A group of researchers studying the relationship between exposure to pesticides and Parkinson’s disease (PD) in a local population identified 110 patients via chart review diagnosed with PD and 220 patients from the same geographical area who were not diagnosed with PD. Twenty-seven PD-diagnosed patients were exposed to pesticides and 19 subjects were in the control group.
Based on this case-control study, what are the odds that a person exposed to pesticides in this area will be diagnosed with PD?
Problem 5
An investigator is studying the efficacy of a new pharmaceutical intervention in preventing atherosclerosis in patients above 50 years of age with risk factors for atherosclerosis but no confirmed diagnosis. Participating patients were randomized to either pharmacologic therapy with the new beta blocker or a placebo. The results show that seven patients develop atherosclerosis with pharmacological therapy and 226 do not. Without pharmacological treatment, 23 patients develop atherosclerosis, and 443 do not.
Based on this information, what is the relative risk reduction of atherosclerosis brought about due to pharmacologic therapy in comparison to the control group?