How reliable and consistent is the MAP RIT score compared to the ALT RIT score?
NWEA conducted a study of more than 1500 students who took ALT and MAP tests in reading, language usage, and mathematics in 2001. The students took a spring ALT test and MAP the following fall. Correlation coefficients for these tests were .85 (math), .83 (reading), and .83 (language usage). In short, scores from students taking MAP correlated very closely with ALT scores for those same students.
The primary difference between MAP and ALT is that the adaptive testing algorithm used in MAP produces lower standard error of measure for the final result. This means that MAP tests should produce slightly more stable results over time than will be produced from ALT tests.
See NWEA National Education Research studies here.