A researcher, interested in the onset of early menses, compared the life experiences and history of 1000 14-year-old girls, half of whom had monthly periods and half of whom did not, to determine what variables might be observed. Which would be the most appropriate categorization of this study?

Correct Answer: C

Rationale: When a study looks at individuals with a particular condition in comparison with those who do not have the disease, based on their exposures to various life situations, it is a retrospective study; that is, the study requires participants to look back at previous experiences. A cross-sectional study examines relationships between potential causal factors and disease at a specific time. A prospective study monitors a group of disease-free individuals to determine if and when disease occurs. A true experiment involves both an experimental group who receives an intervention and a control group who does not receive an intervention.

Correct Answer: B

Rationale: A pandemic (B) is a widespread outbreak across multiple countries or continents (e.g., COVID-19). A is an epidemic, C is localized, and D is seasonal (e.g., flu), not necessarily pandemic.

Correct Answer: C

Rationale: The triad is host (A), agent (B), and environment (D). Vector (C) is a transmission mode, not a core component.

Correct Answer: B

Rationale: Prevalence (B) is total cases at a time (e.g., diabetes prevalence). A is incidence, C is mortality, D is at-risk population.

Correct Answer: C

Rationale: Diabetes (C) is chronic, lasting long-term. Influenza (A) and measles (D) are acute, TB (B) can be chronic but is treatable.