Estimating the reliability of a test split into two parts of equal or unequal length.
When the reliability of test scores must be estimated by an internal consistency method, partition of the test into just 2 parts may be the only way to maintain content equivalence of the parts. If the parts are classically parallel, the Spearman-Brown formula may be validly used to estimate the reliability of total scores. If the parts differ in their standard deviations but are tau equivalent, Cronbach's alpha is appropriate. However, if the 2 parts are congeneric, that is, they are unequal in functional length or they comprise heterogeneous item types, a less well-known estimate, the Angoff-Feldt coefficient, is appropriate. Guidelines in terms of the ratio of standard deviations are proposed for choosing among Spearman-Brown, alpha, and Angoff-Feldt coefficients.
Iowa Testing Programs, The University of Iowa, Iowa City 52242-1529, USA. leonard-feldt@uiowa.edu
Leonard S
LS
Feldt
Richard A
RA
Charter
D000704:Analysis of Variance; D001077:Aptitude Tests / Q000706:statistics & numerical data*; D015982:Bias; D004521:Educational Measurement / Q000706:statistics & numerical data*; D017408:Guidelines as Topic; D006801:Humans; D015233:Models, Statistical; D011581:Psychological Tests / Q000706:statistics & numerical data*; D011594:Psychometrics / Q000706:statistics & numerical data*; D015203:Reproducibility of Results