How does NAEP ensure the comparability of results among the state assessments and between the state and national assessments?

NAEP data are collected using a closely monitored and standardized process. The tight controls that guide the data collection process help ensure the comparability of the results generated for the national and the state assessments. All NAEP sessions use the same assessment booklets and identical administration procedures, and contractor staff members direct all sessions during a single calendar assessment period.

The national sample is a combined sample of students assessed in each participating state, plus an additional sample from the states that did not participate in the state assessment, ensuring that the national sample is representative of the total national student population. The full data set is analyzed together, allowing all data to contribute to the final results and setting a single scale for the assessment. All results are then reported in the scale score metric used for the specific assessment. In years with both national and state assessments in the same subjects, the national sample is a subset of the combined sample of public-school students assessed in each participating state, plus an additional sample from the states that did not participate, and a national nonpublic school sample.