University:
California State University, Northridge
Course:
PSY 427 | Introduction to Psychological Testing
Academic year:

2024
Views:

319

Pages:

9
Author:

Jaydan Simpson

Classical Test Theory Classical Test Theory (CTT) - analyses are the easiest and most widely used form of analyses. The statistics can be computed by readily available statistical packages (or even by hand)  Classical Analyses are performed on the test as a whole rather than on the item and although item statistics can be generated, they apply only to that group of students on that collection of items  Classical Test Theory  CTT is based on the true score model X= T + E  In CTT we assume that the error :  Is normally distributed  Uncorrelated with true score  Has a mean of Zero Classical Test Theory Statistics  Difficulty (item level statistic)  Discrimination (item level statistic)  Reliability (test level statistic) Classical Test Theory vs. Latent Trait Models Classical analysis has the test (not the item) as its basis. Although the statistics generated are often generalised to similar students taking a similar test; they only really apply to those students taking that test  Latent trait models aim to look beyond that at the underlying traits which are producing the test performance. They are measured at item level and provide sample-free measurement  Latent Trait Models Latent trait models have been around since the 1940s, but were not widely used until the 1960s. Although theoretically possible, it is practically unfeasible to use these without specialized software.  They aim to measure the underlying ability (or trait) which is producing the test performance rather than measuring performance per se.  This leads to them being sample-free. As the statistics are not dependant on the test situation which generated them, they can be used more flexibly  Item Response Theory Item Response Theory (IRT) – refers to a family of latent trait models used to establish psychometric properties of items and scales  Sometimes referred to as modern psychometrics because in large-scale education assessment, testing programs and professional testing firms IRT has almost completely replaced CTT as method of choice  IRT has many advantages over CTT that have brought IRT into more frequent use  Three Basics Components of IRT Item Response Function (IRF) – Mathematical function that relates the latent trait to the probability of endorsing an item  Item Information Function – an indication of item quality; an item’s ability to differentiate among respondents  Invariance – position on the latent trait can be estimated by any items with know IRFs and item characteristics are population independent within a linear transformation 