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

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

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, but does not improve survival

Answer 3

Lead-time bias

Question 4

If you want to know if geographic 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 - 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 one point in time

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

Prevalence = incidence x duration

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 divides groups by an exposure and looks for development of disease

Case-control divides groups by a disease and assigns controls, and then goes back and looks for exposures

Question 16

Attributable risk?

Answer 16

The difference in risk in the exposed and unexposed groups (i.e 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 non-exposed group

Question 18

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

Answer 18

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

Question 19

Odds ratio?

Answer 19

Cohort studies: odds of developing the disease in the exposed group divided by the odds of developing the disease in the non exposed group

Case-control: odds that the cases were exposed divided by the odds that the controls were exposed

X-sectional: odds that the exposed group has the disease divided by the odds that the non-exposed group has the disease

Question 20

Most common cancer in men and most common cause of death from cancer in men

Answer 20

Prostate cancer is most common in men; but lung cancer causes more deaths

Question 21

Percentage of cases within 1 standard deviation (SD) of the mean?
2SDs?
3SDs?

Answer 21

68%

95. 4%
96. 7%

Question 22

Birth rate?

Answer 22

Number of live births per 1000 population in 1 year

Question 23

Mortality rate?

Answer 23

Number of deaths per 1000 population in 1 year

Question 24

Neonatal mortality rates?

Answer 24

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

Question 25

Infant mortality rates?

Answer 25

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

Question 26

Maternal mortality rate?

Answer 26

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