Epidemiology

Question 1

How do you interpret the following 95% confidence interval (CI) for a relative risk (RR) of 0.582: 95% CI 0.502, 0.673?

Answer 1

These data are consistent with RRs ranging from 0.502 to 0.673 with 95% confidence (ie, we are confident that the true RR will be between 0.502 and 0.673 95 out of 100 times).

Question 2

Bias introduced into a study when a clinician is aware of the patient’s treatment type.

Answer 2

Observational bias.

Question 3

Bias introduced when screening detects a disease earlier and thus lengthens the time from diagnosis to death.

Answer 3

Lead-time bias.

Question 4

If you want to know if geographical location affects infant mortality rate but most variation in infant mortality is predicted by socioeconomic status, then socioeconomic status is a _____.

Answer 4

Confounding variable.

Question 5

The proportion of people who have the disease and test 􏰁 is the _____.
.

Answer 5

Sensitivity

Question 6

Sensitive tests have few false 􏰂s and are used to rule _____ a disease.
.

Answer 6

Out

Question 7

PPD reactivity is used as a screening test because most people with TB (except those who are anergic) will have a 􏰁 PPD. Highly sensitive or specific?

Answer 7

Highly sensitive for TB. Screening tests with high sensitivity are good for diseases with low prevalence.

Question 8

Chronic diseases such as SLE—higher prevalence or incidence?

Answer 8

Higher prevalence.

Question 9

Epidemics such as influenza—higher prevalence or incidence?

Answer 9

Higher incidence.

Question 10

What is the difference between incidence and prevalence?

Answer 10

Prevalence is the percentage of cases of disease in a population at 1 snapshot in time. Incidence is the percentage of new cases of disease that develop over a given time period among the total population at risk.

Question 11

Cross-sectional survey—incidence or prevalence?
.

Answer 11

Prevalence

Question 12

Cohort study—incidence or prevalence?

Answer 12

Incidence and prevalence.

Question 13

Case-control study—incidence or prevalence?
.

Answer 13

Neither

Question 14

Describe a test that consistently gives identical results, but the results are wrong.

Answer 14

High reliability (precision), low validity (accuracy).

Question 15

Difference between a cohort and a case-control study.

Answer 15

Cohort studies can be used to calculate RR, incidence, and/or odds ratio (OR). Case-control studies can be used to calculate an OR, which is an estimate of RR when the disease prevalence is low

Question 16

Attributable risk?

Answer 16

The difference in risk in the exposed and unexposed groups (ie, the risk that is attributable to the exposure).

Question 17

Relative risk?

Answer 17

Incidence in the exposed group divided by the incidence in the nonexposed group.

Question 18

The results of a hypothetical study found an association between ASA intake and risk of heart disease. How do you interpret an RR of 1.5?

Answer 18

In patients who took ASA, the risk of heart disease was 1.5 times that of patients who did not take ASA.

Question 19

Odds ratio?
In cohort studies, the odds of developing the disease in the exposed group divided by the odds of developing the disease in the nonexposed group.

Answer 19

In case-control studies, the odds that the cases were exposed divided by the odds that the controls were exposed.
In cross-sectional studies, the odds that the exposed group has the disease divided by the odds that the nonexposed group has the disease.

Question 20

In which patients do you initiate colorectal cancer screening early?

Answer 20

Patients with IBD; those with familial adenomatous polyposis (FAP)/ hereditary nonpolyposis colorectal cancer (HNPCC); and those who have first-degree relatives with adenomatous polyps (< 60 years of age) or colorectal cancer.

Question 21

The most common cancer in men and the most common cause of death from cancer in men.

Answer 21

Prostate cancer is the most common cancer in men, but lung cancer causes more deaths.

Question 22

The percentage of cases within 1 SD of the mean? Two SDs? Three SDs?

Answer 22

68%, 95.4%, 99.7%.

Question 23

Birth rate?

Answer 23

Number of live births per 1000 population in 1 year.

Question 24

Mortality rate?

Answer 24

Number of deaths per 1000 population in 1 year.

Question 25

Neonatal mortality rate?

Answer 25

Number of deaths from birth to 28 days per 1000 live births in 1 year.

Question 26

Infant mortality rate?

Answer 26

Number of deaths from birth to 1 year of age per 1000 live births (neonatal + postnatal mortality) in 1 year.

Question 27

Maternal mortality rate?

Answer 27

Number of deaths during pregnancy to 90 days postpartum per 100,000 live births in 1 year