Study guides › P/S › Research Methods & Statistics
Validity, Reliability & Bias
Good conclusions need good measurements and fair samples. You will learn the types of validity and reliability, the common biases and confounds, how sampling methods differ, and why replication matters, so you can find the flaw in any study passage.
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What this chapter covers
- Validity: Internal, External & Construct. Validity asks whether a study measures and concludes what it claims to. Passage questions often hide one validity flaw for you to name.
- Reliability & How It Differs from Validity. Reliability means consistent results. The MCAT loves the trap that a measure can be perfectly reliable and still be wrong.
- Confounds & Types of Bias. Bias questions ask you to name the specific flaw. Learn the source of each bias and the usual fix.
- Sampling, Generalizability & Replication. Who was sampled and whether findings repeat determine whether a result is worth trusting beyond one study.
Key points to know
- Internal validity = causation is trustworthy; external = results generalize
- History, maturation, testing, regression, and attrition threaten internal validity
- Reliability = consistency (random error); validity = accuracy (systematic error)
- Test-retest, inter-rater, internal consistency, parallel forms
- Confound relates to both IV and DV and offers an alternate explanation
- Selection bias concerns who is in the sample; attrition is unequal dropout
- Probability sampling allows generalization; convenience does not
- Stratified sampling matches subgroup proportions
Try a practice question
Which type of validity concerns whether the independent variable actually caused the observed change in the dependent variable?
- Internal validity
- External validity
- Face validity
- Content validity
Show the answer
A. Internal validity is about the correctness of the causal inference within the study. External validity concerns generalization to other people and settings.
Common questions
What does this chapter cover?
Validity, Reliability & Bias covers Validity: Internal, External & Construct, Reliability & How It Differs from Validity, Confounds & Types of Bias, Sampling, Generalizability & Replication.
What should I know first?
Internal validity = causation is trustworthy; external = results generalize History, maturation, testing, regression, and attrition threaten internal validity Reliability = consistency (random error); validity = accuracy (systematic error)
22 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.