To test or not to test: preliminary assessment of normality when comparing two independent samples
Student’s two-sample t test is generally used for comparing the means of two independent samples, for example, two treatment arms. Under the null hypothesis, the t test assumes that the two samples arise from the same normally distributed population with unknown variance. Adequate control of the Typ...
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| Main Authors: | , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
19 June 2012
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| In: |
BMC medical research methodology
Year: 2012, Volume: 12 |
| ISSN: | 1471-2288 |
| DOI: | 10.1186/1471-2288-12-81 |
| Online Access: | Verlag, kostenfrei, Volltext: http://dx.doi.org/10.1186/1471-2288-12-81 Verlag, kostenfrei, Volltext: https://doi.org/10.1186/1471-2288-12-81 
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| Author Notes: | Justine Rochon, Matthias Gondan and Meinhard Kieser |
| Summary: | Student’s two-sample t test is generally used for comparing the means of two independent samples, for example, two treatment arms. Under the null hypothesis, the t test assumes that the two samples arise from the same normally distributed population with unknown variance. Adequate control of the Type I error requires that the normality assumption holds, which is often examined by means of a preliminary Shapiro-Wilk test. The following two-stage procedure is widely accepted: If the preliminary test for normality is not significant, the t test is used; if the preliminary test rejects the null hypothesis of normality, a nonparametric test is applied in the main analysis. |
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| Item Description: | Gesehen am 16.07.2018 |
| Physical Description: | Online Resource |
| ISSN: | 1471-2288 |
| DOI: | 10.1186/1471-2288-12-81 |