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The Shapiro–Wilk test tests the null hypothesis that a sample x 1, ..., x n came from a normally distributed population. The test statistic is = (= ()) = (¯), where with parentheses enclosing the subscript index i is the ith order statistic, i.e., the ith-smallest number in the sample (not to be confused with ).
The Shapiro–Francia test is a statistical test for the normality of a population, based on sample data. It was introduced by S. S. Shapiro and R. S. Francia in 1972 as a simplification of the Shapiro–Wilk test .
The table shown on the right can be used in a two-sample t-test to estimate the sample sizes of an experimental group and a control group that are of equal size, that is, the total number of individuals in the trial is twice that of the number given, and the desired significance level is 0.05. [4]
Martin Bradbury Wilk, OC (18 December 1922 – 19 February 2013) [1] [2] was a Canadian statistician, academic, and the former chief statistician of Canada. In 1965, together with Samuel Shapiro , he developed the Shapiro–Wilk test , which can indicate whether a sample of numbers would be unusual if it came from a Gaussian distribution .
Computations or tables of the Wilks' distribution for higher dimensions are not readily available and one usually resorts to approximations. One approximation is attributed to M. S. Bartlett and works for large m [2] allows Wilks' lambda to be approximated with a chi-squared distribution
The following example is adapted and abridged from Stuart, Ord & Arnold (1999, §22.2).. Suppose that we have a random sample, of size n, from a population that is normally-distributed.
WebPower Free online statistical power analysis (https://webpower.psychstat.org) Free and open source online calculators ( https://powerandsamplesize.com ) PowerUp! provides convenient excel-based functions to determine minimum detectable effect size and minimum required sample size for various experimental and quasi-experimental designs.
Samuel Sanford Shapiro (July 13, 1930 – November 5, 2023) was an American statistician and engineer. He was a professor emeritus of statistics at Florida International University . He was known for his co-authorship of the Shapiro–Wilk test and the Shapiro–Francia test .