On the Choice of Anchor Tests in Equating

The choice of anchor tests is crucial in applications of the nonequivalent groups with anchor test design of equating. Sinharay and Holland (2006, 2007) suggested miditests, which are anchor tests that are content-representative and have the same mean item difficulty as the total test but have a smaller spread of item difficulties. Sinharay and Holland (2006, 2007), Cho, Wall, Lee, and Harris (2010), Fitzpatrick and Skorupski (2016), Liu, Sinharay, Holland, Curley, and Feigenbaum (2011a), Liu, Sinharay, Holland, Feigenbaum, and Curley (2011b), and Yi (2009) found the miditests to lead to better equating than minitests, which are representative of the total test with respect to content and difficulty. However, these findings recently came into question as Trierweiler, Lewis, and Smith (2016) concluded, based on a comparison of correlation coefficients of miditests and minitests with the total test, that making an anchor test a miditest does not generally increase the anchor to total score correlation and recommended the continuation of the practice of using minitests over miditests. Their recommendation raises the question, "Should miditests continue to be considered in practice?" This note defends the miditests by citing literature that favors miditests and then by showing that miditests perform as well as the minitests in most realistic situations considered in Trierweiler etal. (2016), which implies that miditests should continue to be seriously considered by equating practitioners.