Validity
Definition
The degree to which evidence and theory support the interpretation of test scores for a specific purpose; modern standards treat it as unitary, built from multiple evidence sources.
- Framework
- Unitary validity model (Messick / AERA-APA-NCME standards)
- Evidence types
- Content, criterion, construct, and consequential evidence
- Contrast
- Distinct from reliability, which measures consistency not accuracy
- Applies to
- The interpretation for a specific use, not the test itself
Common questions
Why is a test never simply called valid or invalid?+
Validity attaches to a specific interpretation and use of a score, not to the instrument in the abstract. A test can support one inference well, such as screening for cognitive impairment, while supporting a different inference, such as predicting violence risk, poorly.
How does validity differ from reliability in practice?+
Reliability asks whether a test gives consistent scores across administrations or raters. Validity asks whether those scores mean what the examiner claims they mean. A reliable test can still be invalid for a given forensic question if the score does not actually track the construct at issue.
Related terms
- Reliability
- The extent to which a measurement procedure produces the same result when repeated under the same conditions or by a different researcher.
- AUC Statistic
- Area under the receiver operating characteristic curve; the standard criterion-validity metric for forensic risk and malingering instruments, with 0.70 considered a minimum...
- Base Rate
- The prior probability of an event or proposition before specific evidence is considered. In forensic inference, the base rate is the probability...
- BSA 2023 § 39
- Section 39 of the Bharatiya Sakshya Adhiniyam 2023, the provision governing expert opinion evidence in Indian courts. Replaced Indian Evidence Act 1872...
- Consequential Validity
- The fairness and equity implications of test use; includes disparate impact on racial or cultural groups and the systematic bias this may...
- Criterion Validity
- The degree to which test scores predict or correlate with an external criterion; predictive criterion validity is most relevant to forensic instruments.
- Daubert Standard
- The US federal evidentiary standard (Daubert v. Merrell Dow Pharmaceuticals, 1993) requiring that expert testimony be based on scientifically valid methods with...
- Ecological Validity
- The degree to which a measurement or test procedure produces results that generalise from the controlled laboratory context to the real-world condition...
- Incremental Validity
- The improvement in predictive accuracy that a test adds over and above prior information; justifies the cost and burden of additional assessment.
- Interpretivism
- The view that human action has to be understood through the meaning actors themselves attach to it, which requires closeness to lived...
- Operationalisation
- The process of turning an abstract concept, such as fear of crime or recidivism, into a measurable variable with a stated procedure...
- Positive Predictive Value (PPV)
- The probability that a person who tests positive on a risk instrument will actually reoffend. PPV depends on both the instrument's sensitivity...
Explained in these topics
- Foundations of Forensic Assessment and Test Validity
- Quantitative and Qualitative Research Methods in CriminologyThe extent to which a measure or a study actually captures the concept it claims to capture, and the extent to which its causal claims hold up.