A nurse conducted a study of two skin lotions: (1) an inexpensive one and (2) an expensive one. The nurse found that there was a relative risk of 0.7 for skin sores using the inexpensive one and a relative risk of 1.2 using the expensive one. Which skin lotion should the nurse use?

Correct Answer: D

Rationale: A risk factor of less than one means the factor is actually protective, so the inexpensive lotion is helpful in preventing skin sores. A risk factor of more than one means the factor increases risk, so using the expensive lotion increases the probability of getting a skin lesion.

Correct Answer: A

Rationale: Randomization in RCTs (A) balances confounders (e.g., age, sex) across groups, reducing bias and isolating the intervention’s effect. B is false; precision depends on tools, not design alone. C is incorrect; RCTs measure exposure first, outcome later. D is irrelevant; motivation doesn’t ensure causality.

Correct Answer: B

Rationale: Epidemiology studies disease distribution and determinants (B) to inform public health. Vaccine development (A), treatment (C), and training (D) are not its primary aims.

Correct Answer: C

Rationale: Infectious period (C) is when transmission occurs (e.g., flu). A is exposure to symptoms, B is pre-infectious latency, D is post-infectious.

Correct Answer: C

Rationale: Population at risk (C) is those susceptible (e.g., unvaccinated for measles). A is cases, B is immune, D is recovered.