Test Validity and Reliability in Psychological Assessment
VALIDITY AND RELIABILITY IN PSYCHOLOGICAL TESTING
Validity
Validity directly assesses how well a test fulfills its intended function. It requires external criteria, independent of what the test aims to measure.
Types of Validity:
Construct Validity (Theoretical, Structural, or Factorial)
Construct validity examines if the test aligns with the theoretical framework it’s based on and if it effectively operationalizes the construct being measured. This requires accumulating evidence from various sources, such as correlations with similar instruments.
Content Validity
Content validity involves expert judgment and a systematic review of test items to determine if the test covers a representative sample of the behavior domain being measured. This is typically assessed early in test development.
Criterion Validity (Empirical)
Criterion validity refers to the test’s practical use in predicting individual performance in specific activities. There are two main types:
- Concurrent Validity: Assesses if the test provides similar information as other established measures of the same attribute. It’s useful for diagnosing the current state rather than predicting future outcomes.
- Predictive Validity: Evaluates the test’s ability to predict future performance on a relevant criterion. It’s commonly used in personnel selection and classification tests.
Criterion validity is interpreted using correlation coefficients, which indicate the degree of covariation between variables.
Apparent Validity
Apparent validity refers to what the test appears to measure to the test-taker. It’s important for ensuring truthful responses and a positive test-taking attitude.
Reliability
Reliability refers to the consistency of test scores obtained by the same individuals when they take the same test or an equivalent form. It’s closely related to measurement error, as reliability estimates indicate the proportion of score variance due to error.
Methods for Assessing Reliability:
Test-Retest Reliability:
The same test is administered to the same group at two different times, and the correlation between the scores is calculated. This method assumes the group remains stable during the testing interval.
Parallel Forms Reliability:
Two equivalent forms of the test are administered to the same group, and the correlation between the scores is calculated. This method is less common due to the difficulty of creating truly parallel forms.
Internal Consistency:
- Split-Half Reliability: The test is split into two halves, and the correlation between the scores on each half is calculated. This provides an estimate of internal consistency.
- Inter-Item Consistency: The correlations between all items on the test are averaged to assess the overall internal consistency.
Scorer Reliability:
Assesses the consistency of scores assigned by different raters or scorers. This is important for ensuring standardized scoring procedures.
Errors in Measurement
Systematic Bias (Validity)
Systematic bias refers to errors that consistently affect test scores in a particular direction. This can be due to factors such as cultural differences, test adaptation issues, or flaws in the test design. It’s important to ensure test fairness and equivalence across different groups.
Random Measurement Error (Reliability)
Random error refers to unsystematic fluctuations in test scores due to chance factors such as fatigue, mood, or environmental conditions. While it’s impossible to eliminate random error entirely, minimizing it through standardized testing procedures is crucial.
Understanding both validity and reliability is essential for interpreting test scores and ensuring the appropriate use of psychological assessments.