BHS Epidemiology 4

Question 1

Lead-time bias in cancer screening studies causes an apparent improvement in survival because:

Accepted Answer

Survival is measured from diagnosis, which is advanced earlier

Answer

Lead-time bias inflates survival time by starting the clock at an earlier diagnosis without the person actually living longer.

Question 2

Herd immunity is achieved when the proportion of immune individuals in a population reaches:

Accepted Answer

1 − (1/R₀)

Answer

The herd immunity threshold is 1 − 1/R₀; above this fraction, each case on average produces fewer than one new case and the epidemic declines.

Question 3

In a 2×2 contingency table for a case-control study, the measure of association calculated is the:

Accepted Answer

Odds ratio

Answer

Because case-control studies do not follow a population over time, incidence cannot be calculated directly; the odds ratio approximates relative risk.

Question 4

Which of the following is a strength of ecological studies compared to individual-level studies?

Accepted Answer

Can utilize routinely collected population-level data at low cost

Answer

Ecological studies are efficient and inexpensive because they use existing aggregate data such as disease registries and census records.

Question 5

A study examining disease rates in populations with different fluoride levels in water is an example of:

Accepted Answer

Ecological study

Answer

Ecological studies compare disease rates across populations defined by average exposure levels rather than measuring individual exposures.

BHS - Bachelor of Health Science Practice Test

BHS - Bachelor of Health Science Practice Test

BHS Epidemiology 4