**Question:** Epidemiological survey of 'at risk' is called

A. Prevalence survey
B. Incidence survey
C. Case-control study
D. Cross-sectional study

**Correct Answer:** D. Cross-sectional study

**Core Concept:** An epidemiological survey is a research design used to study the distribution and determinants of health-related factors or outcomes in a population. 'At risk' refers to individuals or groups with an increased likelihood of developing a specific disease or condition due to certain risk factors.

**Why the Correct Answer is Right:** A cross-sectional study is a type of epidemiological survey that involves assessing a sample of the population at a single point in time. It provides information on the prevalence of a health condition or risk factors in a specific population. In the context of epidemiological surveys of 'at risk' individuals, a cross-sectional study would be appropriate as it assesses the current status of the population regarding disease risk.

**Why Each Wrong Option is Incorrect:**

A. Prevalence survey: This refers to a study that examines the presence or prevalence of a disease or condition in a population at a specific point in time. It is not suitable for epidemiological surveys of 'at risk' individuals because it only provides information on the current status of the population and doesn't address the underlying risk factors.

B. Incidence survey: This type of study focuses on the occurrence or development of a disease or condition over a specific period. It is not relevant for epidemiological surveys of 'at risk' individuals, as it deals with the occurrence of new cases, not the assessment of risk factors and prevalence in the population.

C. Case-control study: This study design compares cases (individuals with a particular disease or condition) with controls (healthy individuals or those without the condition). It is not suitable for epidemiological surveys of 'at risk' individuals, as it focuses on comparing cases with controls rather than assessing the overall risk factors and prevalence in the population.

**Clinical Pearl:** Understanding the appropriate study design for epidemiological surveys is crucial for conducting accurate investigations of disease risk factors and prevalence in a population. Cross-sectional studies are best suited for assessing the current status of a population's health condition and risk factors, while incidence and case-control studies focus on different aspects of disease occurrence and comparison, respectively.