Question at position 37 Why do individual differences (e.g., age, baseline ability, personality) typically not threaten internal validity in a well-designed experiment, even if they influence the dependent variable?Because individual differences are relevant to external validity but not internal validityBecause individual differences are eliminated once the dependent variable is measuredBecause individual differences only affect correlational, not experimental, studiesBecause random assignment distributes individual differences across conditions, making them unlikely to account for observed group differencesClear my selection

Question

BlackTom AI · Accepted Answer

Random assignment ensures that individual differences are, on average, spread evenly across experimental conditions.

1) Relevant knowledge points and concepts:
- Internal validity: the degree to which observed effects on the dependent variable (DV) can be attributed to the independent variable (IV) rather than confounds.
- Individual differences (age, baseline ability, personality) are subject variables that can influence the DV but only become threats to internal validity if they systematically covary with the IV (i.e., are confounded).
- Random assignment: allocating participants to conditions by chance so that, on average, all uncontrolled variables are balanced across groups.

2) Step-by-step reasoning:
- Suppose individual differences affect the DV. If participants with higher baseline ability were all placed in one condition, differences in DV could be due to ability rather than the IV — a confound that threatens internal validity.
- With proper random assignment, each participant has an equal chance of being in any condition. This makes it unlikely that any particular individual-difference characteristic will concentrate systematically in one group.
- Therefore, group differences in the DV are unlikely to be explained by those individual differences; they are more plausibly due to the manipulated IV.

3) Calculations: not applicable here; the logic is probabilistic rather than numeric. Larger sample sizes improve the chance that random assignment balances individual differences.

4) Why the correct answer is correct:
Because random assignment distributes individual differences across conditions, these differences are not systematically linked with the IV and thus are unlikely to account for observed group differences — preserving internal validity.

5) Why the other options are incorrect:
- Option 1: Individual differences can affect internal validity if not controlled; they are not relevant only to external validity.
- Option 2: Measuring the DV does not eliminate preexisting individual differences or their potential confounding role.
- Option 3: Individual differences can influence both correlational and experimental studies; the key in experiments is random assignment, not that they "only affect" correlational designs.

6) Conclusion:
The correct choice is the option stating that random assignment distributes individual differences across conditions, making them unlikely to account for observed group differences, which matches the provided answer.

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