Unidimensionality and local independence are two common assumptions of item response theory. The former implies that all items measure a common latent trait, while the latter implies that responses are independent, conditional on respondents' location on the latent trait. Yet, few tests are truly unidimensional. Unmodeled dimensions may result in…

The purpose of the present article is to report on a large-scale investigation of six school districts' implementation of an initiative aimed at reducing dropout rates by improving reading achievement in the middle grades. Data for the Middle School Intervention Project (MSIP) were collected in 25 middle schools across the state of Oregon. We…