NotesFAQContact Us
Search Tips
Peer reviewed Peer reviewed
Direct linkDirect link
ERIC Number: EJ921811
Record Type: Journal
Publication Date: 2011-Apr
Pages: 27
Abstractor: As Provided
Reference Count: 41
ISSN: ISSN-1076-9986
Outliers in Questionnaire Data: Can They Be Detected and Should They Be Removed?
Zijlstra, Wobbe P.; van der Ark, L. Andries; Sijtsma, Klaas
Journal of Educational and Behavioral Statistics, v36 n2 p186-212 Apr 2011
Outliers in questionnaire data are unusual observations, which may bias statistical results, and outlier statistics may be used to detect such outliers. The authors investigated the effect outliers have on the specificity and the sensitivity of each of six different outlier statistics. The Mahalanobis distance and the item-pair based outlier statistics were found to have the best combination of specificity and sensitivity. Next, it was investigated how outliers influenced the bias in the percentile rank score, Cronbach's alpha, and the validity coefficient. Outliers due to random responding and faking produced considerable bias, and outliers due to extreme responding produced little bias. Finally, the influence of removing discordant observations on bias was studied. Removing observations due to random responding identified by means of the Mahalanobis distance, the local outlier factor, and the item-pair based outlier statistic reduced bias. (Contains 5 tables and 1 figure.)
SAGE Publications. 2455 Teller Road, Thousand Oaks, CA 91320. Tel: 800-818-7243; Tel: 805-499-9774; Fax: 800-583-2665; e-mail:; Web site:
Publication Type: Journal Articles; Reports - Research
Education Level: N/A
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A