Testing for local dependence in Rasch's multiplicative gamma model for speed tests

The author considers a latent trait model for the response time on a (set of) pure speed test(s), the multiplicative gamma model (MGM), which is based on the assumption that the test response times are approximately gamma distributed, with known index parameters and scale parameters depending on subject ability and test difficulty parameters. Like any other parametric latent trait model, the MGM is based on strong assumptions. One of these assumptions is local independence. Two statistical tests for checking if the local independence assumption holds are compared, using generated and empirical data.