Original Research

Overcoming the effects of differential skewness of test items in scale construction

Johann M. Schepers
SA Journal of Industrial Psychology | Vol 30, No 4 | a170 | DOI: https://doi.org/10.4102/sajip.v30i4.170 | © 2004 Johann M. Schepers | This work is licensed under CC Attribution 4.0
Submitted: 26 October 2004 | Published: 26 October 2004

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Johann M. Schepers, Rand Afrikaans University, South Africa

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Abstract

The principal objective of the study was to develop a procedure for overcoming the effects of differential skewness of test items in scale construction. It was shown that the degree of skewness of test items places an upper limit on the correlations between the items, regardless of the contents of the items. If the items are ordered in terms of skewness the resulting inter correlation matrix forms a simplex or a pseudo simplex. Factoring such a matrix results in a multiplicity of factors, most of which are artifacts. A procedure for overcoming this problem was demonstrated with items from the Locus of Control Inventory (Schepers, 1995). The analysis was based on a sample of 1662 first year university students.

Opsomming
Die hoofdoel van die studie was om ’n prosedure te ontwikkel om die gevolge van differensiële skeefheid van toetsitems, in skaalkonstruksie, teen te werk. Daar is getoon dat die graad van skeefheid van toetsitems ’n boonste grens plaas op die korrelasies tussen die items ongeag die inhoud daarvan. Indien die items gerangskik word volgens graad van skeefheid, sal die interkorrelasiematriks van die items ’n simpleks of pseudosimpleks vorm. Indien so ’n matriks aan faktorontleding onderwerp word, lei dit tot ’n veelheid van faktore waarvan die meerderheid artefakte is. ’n Prosedure om hierdie probleem te bowe te kom, is gedemonstreer met behulp van die items van die Lokus van Beheer-vraelys (Schepers, 1995). Die ontledings is op ’n steekproef van 1662 eerstejaaruniversiteitstudente gebaseer.


Keywords

Differential skewness; Scale construction; Test items

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