Classical Test Theory vs. Generalized Theory

Attribute	Classical Test Theory	Generalized Theory
Assumption	Assumes that observed scores are composed of true scores and error	Extends the assumptions of Classical Test Theory by considering additional sources of error
Reliability	Focuses on internal consistency reliability	Considers various sources of error and their impact on reliability
Validity	Primarily concerned with construct validity	Expands the concept of validity to include various types such as content, criterion-related, and construct validity
Measurement Error	Assumes that measurement error is random and independent of true scores	Considers various sources of error, including systematic and random error
Item Response Theory	Does not incorporate item response theory	Can incorporate item response theory models for more accurate measurement

Definition

Classical Test Theory (CTT) and Generalized Theory (GT) are two approaches used in psychometrics to assess the reliability and validity of psychological tests. CTT is a traditional approach that focuses on the observed scores of individuals, while GT is a more modern approach that considers the latent traits underlying test performance.

Reliability

In CTT, reliability is typically assessed using measures such as Cronbach's alpha, which estimates the internal consistency of a test. This measure is based on the assumption that all items in a test measure the same underlying construct. On the other hand, GT uses methods such as item response theory to estimate reliability by modeling the relationship between item difficulty, person ability, and item discrimination.

Validity

Validity in CTT is often assessed through methods such as factor analysis, which examines the relationship between test items and underlying constructs. CTT also considers content validity, which ensures that a test measures what it is intended to measure. In contrast, GT uses structural equation modeling to assess construct validity by testing the relationships between latent traits and observed variables.

Scalability

One of the limitations of CTT is that it assumes that test items are equally reliable and that test scores are normally distributed. This can be problematic when dealing with tests that have varying levels of difficulty or when test scores are skewed. GT, on the other hand, allows for the estimation of item difficulty and person ability separately, making it more scalable to tests with varying item characteristics.

Flexibility

CTT is often criticized for its lack of flexibility in handling complex test structures and non-linear relationships between items and constructs. GT, on the other hand, is more flexible in modeling complex relationships between latent traits and observed variables. This flexibility allows for the development of more sophisticated measurement models that can better capture the underlying structure of psychological tests.

Interpretability

One of the strengths of CTT is its simplicity and ease of interpretation. Test scores in CTT are typically reported as raw scores or standardized scores, making them easy to understand for practitioners and researchers. GT, on the other hand, often involves more complex statistical models and may require specialized training to interpret the results accurately. This can make GT less accessible to those without a strong background in psychometrics.

Conclusion

In conclusion, both Classical Test Theory and Generalized Theory have their strengths and limitations when it comes to assessing the reliability and validity of psychological tests. While CTT is more straightforward and easier to interpret, GT offers greater scalability and flexibility in modeling complex relationships between test items and latent traits. Researchers and practitioners should consider the specific needs of their research or assessment goals when choosing between these two approaches.