A community health clinic put a tax levy on the ballot. An angry man asks a nurse, 'How can you ask me to pay taxes to buy immunizations for parents who do not want to pay for their kids to get their shots?' Which is the most appropriate response by the nurse?

Correct Answer: C

Rationale: Herd immunity is a state in which those not immune to an infectious agent will be protected if a certain proportion (generally considered to be $80 \%$ ) of the population has been vaccinated or is otherwise immune. If most persons are immune, it will be difficult for an infectious disease to spread.

Correct Answer: B

Rationale: Effectiveness of Healthy People 2020 depends on the availability of reliable baseline and continuing data to characterize health problems and evaluate goal achievement. Surveillance is crucial. Without surveillance data, there is no relatable data available. Increased financing will not assist in determining if the health of Americans is improving. Although it is important for individuals to be willing to share health information so that data collection can be completed, individual health information alone will not be an effective determinant of the health of Americans.

Correct Answer: C

Rationale: Nutritional epidemiology studies the relationship between diet and health outcomes in populations. Choice A addresses the role of nutritional factors in disease causation (e.g., linking high fat intake to heart disease), a core focus. Choice B addresses how dietary changes can improve health (e.g., increasing fiber to reduce colon cancer risk), also a key area. Since both are accurate and central to the field, C is correct. D is incorrect as both A and B are valid.

Correct Answer: D

Rationale: Randomized controlled trials (RCTs, D) establish causality by controlling confounding through randomization and intervention. Cohort (B) and case-control (C) studies suggest associations, while cross-sectional (A) studies assess prevalence, not causation.

Correct Answer: C

Rationale: A control group (C) provides a baseline to compare outcomes, assessing exposure effects. A and B apply to trials, D is unrelated.