The authors detail a computer-simulation study they conducted to investigate the amount of uncertainty added to NAEP estimates by equating error, under three different equating methods, and while varying a number of factors that might affect accuracy of equating. Data from past NAEP administrations were used to guide the simulations, and error due to equating was estimated empirically. It is the authors' conclusion that the merits of less biased measurements may outweigh the problems caused by slight adjustments to previously reported scores. They recommend that long-term trend lines be periodically reanalyzed using methods such as multiple-group IRT that can minimize such biases.
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