The Effects of Heterogeneous Item Distributions on Reliability

Craig Enders, Deborah L. Bandalos

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

A computer simulation was designed to investigate the degree to which coefficient alpha is affected by the inclusion of items with different distribution shapes within a unidimensional scale. Theoretical scales were generated that combined different numbers of normal, moderately skewed, extremely skewed, and leptokurtic items. This process was repeated using different numbers of response categories (3, 5, 7, and 9), and different levels of interitem correlation (.25, .50, and .75). Results indicated that reliability did not decrease dramatically as a result of utilizing differentially shaped items within a scale; the largest decreases came about when utilizing highly skewed items. However, these results were moderated by the correlational structure and by the number of response categories. Utilizing differentially shaped items brought about the largest decreases in reliability when the interitem correlations were low and when the number of response categories was small. Conversely, reliability was least affected when the interitem correlations were high and when the number of response categories was large. It was suggested that the practice of deleting items from a scale on the basis of distributional nonnormality may adversely affect scale validity with no appreciable increase in reliability.

Original languageEnglish (US)
Pages (from-to)133-150
Number of pages18
JournalApplied Measurement in Education
Volume12
Issue number2
StatePublished - 1999
Externally publishedYes

Fingerprint

Reproducibility of Results
Computer Simulation
computer simulation
inclusion

ASJC Scopus subject areas

  • Psychology (miscellaneous)
  • Developmental and Educational Psychology
  • Education

Cite this

The Effects of Heterogeneous Item Distributions on Reliability. / Enders, Craig; Bandalos, Deborah L.

In: Applied Measurement in Education, Vol. 12, No. 2, 1999, p. 133-150.

Research output: Contribution to journalArticle

Enders, C & Bandalos, DL 1999, 'The Effects of Heterogeneous Item Distributions on Reliability', Applied Measurement in Education, vol. 12, no. 2, pp. 133-150.
Enders, Craig ; Bandalos, Deborah L. / The Effects of Heterogeneous Item Distributions on Reliability. In: Applied Measurement in Education. 1999 ; Vol. 12, No. 2. pp. 133-150.
@article{ef88b9ef73b14e8db4df88863244bbd6,
title = "The Effects of Heterogeneous Item Distributions on Reliability",
abstract = "A computer simulation was designed to investigate the degree to which coefficient alpha is affected by the inclusion of items with different distribution shapes within a unidimensional scale. Theoretical scales were generated that combined different numbers of normal, moderately skewed, extremely skewed, and leptokurtic items. This process was repeated using different numbers of response categories (3, 5, 7, and 9), and different levels of interitem correlation (.25, .50, and .75). Results indicated that reliability did not decrease dramatically as a result of utilizing differentially shaped items within a scale; the largest decreases came about when utilizing highly skewed items. However, these results were moderated by the correlational structure and by the number of response categories. Utilizing differentially shaped items brought about the largest decreases in reliability when the interitem correlations were low and when the number of response categories was small. Conversely, reliability was least affected when the interitem correlations were high and when the number of response categories was large. It was suggested that the practice of deleting items from a scale on the basis of distributional nonnormality may adversely affect scale validity with no appreciable increase in reliability.",
author = "Craig Enders and Bandalos, {Deborah L.}",
year = "1999",
language = "English (US)",
volume = "12",
pages = "133--150",
journal = "Applied Measurement in Education",
issn = "0895-7347",
publisher = "Routledge",
number = "2",

}

TY - JOUR

T1 - The Effects of Heterogeneous Item Distributions on Reliability

AU - Enders, Craig

AU - Bandalos, Deborah L.

PY - 1999

Y1 - 1999

N2 - A computer simulation was designed to investigate the degree to which coefficient alpha is affected by the inclusion of items with different distribution shapes within a unidimensional scale. Theoretical scales were generated that combined different numbers of normal, moderately skewed, extremely skewed, and leptokurtic items. This process was repeated using different numbers of response categories (3, 5, 7, and 9), and different levels of interitem correlation (.25, .50, and .75). Results indicated that reliability did not decrease dramatically as a result of utilizing differentially shaped items within a scale; the largest decreases came about when utilizing highly skewed items. However, these results were moderated by the correlational structure and by the number of response categories. Utilizing differentially shaped items brought about the largest decreases in reliability when the interitem correlations were low and when the number of response categories was small. Conversely, reliability was least affected when the interitem correlations were high and when the number of response categories was large. It was suggested that the practice of deleting items from a scale on the basis of distributional nonnormality may adversely affect scale validity with no appreciable increase in reliability.

AB - A computer simulation was designed to investigate the degree to which coefficient alpha is affected by the inclusion of items with different distribution shapes within a unidimensional scale. Theoretical scales were generated that combined different numbers of normal, moderately skewed, extremely skewed, and leptokurtic items. This process was repeated using different numbers of response categories (3, 5, 7, and 9), and different levels of interitem correlation (.25, .50, and .75). Results indicated that reliability did not decrease dramatically as a result of utilizing differentially shaped items within a scale; the largest decreases came about when utilizing highly skewed items. However, these results were moderated by the correlational structure and by the number of response categories. Utilizing differentially shaped items brought about the largest decreases in reliability when the interitem correlations were low and when the number of response categories was small. Conversely, reliability was least affected when the interitem correlations were high and when the number of response categories was large. It was suggested that the practice of deleting items from a scale on the basis of distributional nonnormality may adversely affect scale validity with no appreciable increase in reliability.

UR - http://www.scopus.com/inward/record.url?scp=0033459384&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0033459384&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:0033459384

VL - 12

SP - 133

EP - 150

JO - Applied Measurement in Education

JF - Applied Measurement in Education

SN - 0895-7347

IS - 2

ER -