Sample Size Evaluation: A study must have a sufficiently large sample to ensure that the results are representative of the broader population and to reduce the margin of error.
Demographic Analysis: The sample must match the target population; for example, data from a study on elderly men cannot be directly applied to young women.
Controlling Variables: Researchers attempt to isolate the effect of a single risk factor by ensuring other variables (like diet or exercise) are consistent across groups.
Ethical Constraints: Since it is unethical to deliberately expose humans to harmful factors in controlled experiments, researchers must rely on observational data from people's existing lifestyles.
| Feature | Correlation | Causation |
|---|---|---|
| Definition | Variables move together | One variable triggers the other |
| Evidence | Statistical association | Requires mechanism and control |
| Example | Ice cream sales and drowning | Smoking and lung tissue damage |
Evaluate the Source: Always check if the study mentions its sample size and whether the participants represent the group the conclusion is about.
Look for 'Third Variables': If a question asks you to evaluate a conclusion, suggest potential confounding variables that the researchers might have missed, such as genetics or environment.
Check the OR Value: Remember that an of is a very weak association, whereas an of is a much stronger indicator of a risk factor.
Question Causality: If a data set shows two trends following the same path, never state they are 'causal' unless the data explicitly provides evidence of a mechanism.
The 'Small Sample' Trap: Students often accept results from small groups as universal truths, ignoring the high probability of sampling error.
Ignoring the Baseline: A high Odds Ratio might seem alarming, but if the original disease is extremely rare, the absolute risk might still be very low.
Overgeneralization: Applying findings from one specific demographic (e.g., professional athletes) to the general public is a frequent error in data interpretation.