Equating in item response theory Equating

figure 1: test characteristic curves showing relationship between total score , person location 2 different tests in relation common scale. in example total of 37 on assessment 1 equates total of 34.9 on assessment 2 shown vertical line

in item response theory, person locations estimated on scale; i.e. locations estimated in relation unit , origin. common in educational assessment employ tests in order assess different groups of students intention of establishing common scale equating origins, , units, of scales obtained response data different tests. process referred equating or test equating.

in item response theory, 2 different kinds of equating horizontal , vertical equating. vertical equating refers process of equating tests administered groups of students different abilities, such students in different grades (years of schooling). horizontal equating refers equating of tests administered groups similar abilities; example, 2 tests administered students in same grade in 2 consecutive calendar years. different tests used avoid practice effects.

in terms of item response theory, equating special case of more general process of scaling, applicable when more 1 test used. in practice, though, scaling implemented separately different tests , scales subsequently equated.

a distinction made between 2 methods of equating; common person , common item equating. common person equating involves administration of 2 tests common group of persons. mean , standard deviation of scale locations of groups on 2 tests equated using linear transformation. common item equating involves use of set of common items referred anchor test embedded in 2 different tests. mean item location of common items equated.