Regarding the advantages of cohort studies compared to case-control studies, all of the following are true EXCEPT:

Question

Accepted Answer

D. Cohort studies are more efficient for studying rare diseases. ## Understanding Cohort vs Case-Control Study Efficiency

### Why Option 1 is Correct (The Exception)

**Key Point:** Case-control studies are MORE efficient for studying rare diseases, not cohort studies. Cohort studies are inefficient for rare outcomes because you must follow a large population for extended periods to observe few events.

### Comparison of Study Designs for Rare Diseases

| Feature | Cohort Study | Case-Control Study |
|---------|--------------|--------------------|
| Efficiency for rare diseases | Poor (need huge n) | Excellent (select cases directly) |
| Time to completion | Long (prospective) | Short (retrospective) |
| Cost for rare outcomes | High | Low |
| Temporal sequence | Clear | Inferred |

### Why the Other Options are Correct

**Option 0 (Temporal relationship):** Cohort studies follow exposed and unexposed groups forward in time, establishing clear temporal precedence — exposure occurs before outcome.

**Option 2 (Incidence & RR):** Cohort studies directly measure incidence rates in exposed and unexposed groups, allowing calculation of relative risk (RR = Incidence~exposed~ / Incidence~unexposed~). Case-control studies cannot calculate true incidence or RR; they calculate odds ratio (OR) instead.

**Option 3 (Multiple outcomes):** A single cohort can be followed for many different health outcomes from one or more exposures — a major advantage for hypothesis generation and efficiency.

### High-Yield Mnemonic

**"RARE = Case-Control; COMMON = Cohort"**
- **R**are disease → **A**llocate cases → **R**etrospective → **E**fficient
- Cohort: good for common outcomes, poor for rare ones

**Clinical Pearl:** In India, case-control studies of rare cancers (e.g., mesothelioma from asbestos exposure) are far more practical than recruiting a massive cohort and waiting years for disease development.

[cite:Park 26e Ch 8]

Answer

A. Cohort studies allow calculation of incidence and relative risk directly

Answer

B. Cohort studies can establish temporal relationship between exposure and outcome

Answer

C. Cohort studies can evaluate multiple outcomes from a single exposure

Regarding the advantages of cohort studies compared to case-control studies, all of the following are true EXCEPT:

Explanation

Understanding Cohort vs Case-Control Study Efficiency

Why Option 1 is Correct (The Exception)

Comparison of Study Designs for Rare Diseases

Why the Other Options are Correct

High-Yield Mnemonic

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Feature	Cohort Study	Case-Control Study
Efficiency for rare diseases	Poor (need huge n)	Excellent (select cases directly)
Time to completion	Long (prospective)	Short (retrospective)
Cost for rare outcomes	High	Low
Temporal sequence	Clear	Inferred