topic Re: Manual Calculation of the Shapiro-Wilk Test Statistic in Discussions

Manual Calculation of the Shapiro-Wilk Test Statistic

PatrickGiuliano — Tue, 08 Jan 2019 01:15:30 GMT

Hello Everyone,

Does anyone know how to implement manual calculation of the Shapiro-Wilk test statistic in JMP?

Using JSL script and/ or column formulas?

I know that JMP natively does this calculation natively in Analyze>Distribution and then Continuous Fit>Normal>Goodness of Fit, but I'm trying to reproduce the calculated value of the test statistic in order to understand it's basis with greater depth.

There are a number of useful clues in references online, but I'm having some difficulty putting the pieces together:

https://en.wikipedia.org/wiki/Shapiro%E2%80%93Wilk_test#cite_note-8

Here's the basis for it summarized nicely from Wikepedia link above:

Also some helpful clues here using MS Excel.

http://www.real-statistics.com/tests-normality-and-symmetry/statistical-tests-normality-symmetry/shapiro-wilk-test/

Re: Manual Calculation of the Shapiro-Wilk Test Statistic

txnelson — Tue, 08 Jan 2019 03:54:32 GMT

Here is a link that does a step by step calculation that you might be able to use.

http://blog.excelmasterseries.com/2015/05/how-to-create-completely-automated_4.html

Re: Manual Calculation of the Shapiro-Wilk Test Statistic

gzmorgan0 — Wed, 09 Jan 2019 18:43:20 GMT

Ignore this...I did not read your request very closely...sorry

~~JMP calculates the Shapiro-Wilk's test.~~

~~Open a data table.~~
~~Go to Help > Statistics Index> find Shapiro-Wilk test for normality on the left, then press launch~~
~~Select which columns of your table to be tested~~

~~The test is available in JMP PRO 12 and higher.~~

~~It is the Goodnes of Fit test for a Normal Fit. The JSL is~~

Distribution(
	Continuous Distribution(
		Column( :height ),
		Fit Distribution( Normal( Goodness of Fit( 1 ) ) )
	)
);

Re: Manual Calculation of the Shapiro-Wilk Test Statistic

gzmorgan0 — Thu, 10 Jan 2019 10:31:32 GMT

@PatrickGiuliano I am not sure why you would want to do this manually, when you have JMP that can produce the statistics and you can extract it from a report. A simulation where the sample size is the same so the weight coefficients are the same, meaning the weights are calculated once and used many times, might be a good scenario for doing this by hand/matrix.

That said, I found references for the coefficients and an algorithm to get them. The references are reported in the attached script. Here are the results of two tests with N=40.

Re: Manual Calculation of the Shapiro-Wilk Test Statistic

PatrickGiuliano — Sat, 12 Jan 2019 01:02:52 GMT

Thank you this is excellent.