Additional file 1.

Appendix A. Generating and Estimated Item Parameters for the Two Simulated Item Banks (Validation data) Based on the One-and Two-Parameter IRT Models, Respectively. 1PL = one-parameter item response model; 2PL = two-parameter item response model; α = simulated discrimination parameter; β = simulated difficulty parameter; = estimated discrimination parameter; <a onClick="popup('http://www.biomedcentral.com/1471-2288/12/124/mathml/M3','MathML',630,470);return false;" target="_blank" href="http://www.biomedcentral.com/1471-2288/12/124/mathml/M3">View MathML</a>= estimated difficulty parameter.

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Riley and Carle BMC Medical Research Methodology 2012 12:124   doi:10.1186/1471-2288-12-124