Commingled Samples: A Neglected Source of Bias in Reliability Analysis  

Oleh:

Waller, Niels G.

Jenis: Article from Journal - ilmiah internasional
Dalam koleksi: Applied Psychological Measurement vol. 32 no. 3 (May 2008), page 211-223.
Topik: coefficient alpha; reliability; measurement bias
Fulltext: 211.pdf (221.6KB)

Isi artikel

Reliability is a property of test scores from individuals who have been sampled from a welldefined population. Reliability indices, such as coefficient a and related formulas for internal consistency reliability (KR-20, Hoyt’s reliability), yield lower bound reliability estimates when (a) subjects have been sampled from a single population and when (b) test items are congeneric (i.e., when items are sampled from a single latent dimension). However, when samples are commingled—that is, when they are composed of scores that are drawn from multiple populations— coefficient a and related indices can be severely biased. In most cases the bias inflates a; in other cases a is attenuated. Equations are derived for elucidating this bias in two-group mixture distributions.

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