Linking overview With item response theory (IRT), the ability scale is arbitrarily defined (commonly mean of 0 and sd of 1). Linking is useful to help place individual ability and IRT item parameters on the same scale. Particularly when two forms are administered to non-equivalent groups. Four linking methods are common: Mean/Mean Mean/Sigma Haebara Stocking Lord Linking Transformation Linking Designs Random Groups Single group with counterbalancing Common-item nonequivalent group design More details in Kolen & Brennan (2014).
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