How Small Is Big: Sample Size and Skewness

Article

Piovesana, Adina and Senior, Graeme. 2018. "How Small Is Big: Sample Size and Skewness." Assessment. 25 (6), pp. 793-800. https://doi.org/10.1177/1073191116669784
Article Title

How Small Is Big: Sample Size and Skewness

ERA Journal ID6106
Article CategoryArticle
AuthorsPiovesana, Adina (Author) and Senior, Graeme (Author)
Journal TitleAssessment
Journal Citation25 (6), pp. 793-800
Number of Pages8
Year2018
Place of PublicationUnited States
ISSN1073-1911
1552-3489
Digital Object Identifier (DOI)https://doi.org/10.1177/1073191116669784
Web Address (URL)https://journals.sagepub.com/doi/10.1177/1073191116669784
Abstract

Sample sizes of 50 have been cited as sufficient to obtain stable means and standard deviations in normative test data. The influence of skewness on this minimum number, however, has not been evaluated. Normative test data with varying levels of skewness were compiled for 12 measures from 7 tests collected as part of ongoing normative studies in Brisbane, Australia. Means and standard deviations were computed from sample sizes of 10 to 100 drawn with replacement from larger samples of 272 to 973 cases. The minimum sample size was determined by the number at which both mean and standard deviation estimates remained within the 90% confidence intervals surrounding the population estimates. Sample sizes of greater than 85 were found to generate stable means and standard deviations regardless of the level of skewness, with smaller samples required in skewed distributions. A formula was derived to compute recommended sample size at differing levels of skewness.

Keywordsminimum sample sizes, normative data, skewness, psychometrics, psychological assessment
ANZSRC Field of Research 2020520299. Biological psychology not elsewhere classified
520503. Personality and individual differences
Public Notes

File reproduced in accordance with the copyright policy of the publisher/author.

Byline AffiliationsUniversity of Southern Queensland
USQ Centre for Psychological Assessment
Institution of OriginUniversity of Southern Queensland
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