1. Validity Validity of measurement Validity of research
Does it measure what it is supposed to?
Validity of research
Does it prove what it is supposed to?
(Does it support the conclusion that it is supposed to?)

2. Validity of Research Internal Validity Construct Validity
Does the IV (and not some other factor) really cause the changes in the DV?
Ruling out other causes (confounds)
Construct Validity
Does the study support the theory it is supposed to and no other theories?
Ruling out other theories (alternative explanations)
External Validity
Do the results generalize to other people?
Statistical Validity
Does the IV cause the changes in the DV, or could they be due to chance?

3. The two kinds of Construct Validity
Construct validity of measures
Does it measure what it is supposed to and nothing else?
Construct validity of research
Does it support the theory it is supposed to and no other theories?

4. Threats to Validity Internal Validity: Confounds
Construct Validity: Ambiguity
External Validity: Uniqueness
Statistical Validity: Insufficient Power*
* and improper use of statistical techniques

5. Threats to Internal Validity: Confounds
History
Maturation
Testing effects (e.g.: practice effects)
Selection bias (in assigning to conditions)
Mortality
Regression to the mean

6. Threats to Construct Validity: Ambiguity
Loose connection between theory and method (poor operational definition of theoretical concepts)
Ambiguous effects of IVs
If participants interpret the instructions differently than intended
“Good subject” effects
Evaluation apprehension

7. Threats to External Validity: Uniqueness
External validity = generalizability
Non-representative samples
Changes over time
“Ecological validity” – does the result transfer to the real world from the laboratory?
The more unique the experimental situation and the sample, the less generalizable the results are likely to be

8. Threats to Statistical Validity: Insufficient Power
Too small a sample size makes it harder to tell whether an effect is due to chance or not
Other threats besides low power: There are many ways that the improper use of statistical techniques can lead to invalid conclusions.