

AM is a statistical software package for analyzing data from complex samples, especially largescale assessments such as the National Assessment of Educational Progress (NAEP) and the Third International Mathematics and Science Studies (TIMSS). From its origin as a specialized tool for analyzing largescale assessment data, AM has evolved into a more generalized and growing tool for analyzing data from complex samples in general. Originally, AM was developed to estimate regression models through marginal maximum likelihood (MML). Because largescale assessments are often lowstakes assessments for students, students are usually asked to respond to only a few items; each student sees only part of the whole test. Otherwise, they would be unlikely to expend real effort on any items. As a result, individual test scores are subject to substantial measurement error, which would bias many statistical estimates. Rather than assign each student an errorfilled score, MML procedures represent each student’s proficiency as a probability distribution over all possible scores. MML procedures use these probability distributions in the estimation process. Another characteristic of largescale assessments has led to a wider applicability of AM—they almost always draw a sample from a complex design. AM automatically provides appropriate standard errors for complex samples using a Taylorseries approximation. This happens automatically even when new procedures are added to the software. Over time, the software has grown to offer a set of nonMML statistics, including regression, probit, logit, crosstabs, and other statistics that are useful for survey data in general. The American Institutes for Research is committed to keeping AM available as a free and growing tool for the research community. Visit this web site for further information, updates, and technical support. 
