Hi. Here is what I heard back:
"Yes, both NPAR TESTS and NPTESTS use an exact binomial distribution for N <= 25, and a normal approximation Z statistic when N > 25 for the sign test. Both also offer the Wilcoxon matched-pairs signed-rank test as a separate test option."
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Rick Marcantonio
Quality Assurance
IBM
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Original Message:
Sent: Wed March 08, 2023 09:36 AM
From: Clifton Hamilton
Subject: Sign Test in SPSS
Hi Rick,It is well-published that SPSS uses the binomial distribution when conducting a sign test. It is also understood that when there are more than 25 non-tied pairs, a z value is estimated for this test. Can you ask your statisticians if this is always true? I am asking because, as Hollander & Wolfe (1999) suggest, the Wilcoxon signed rank T-plus distribution can also be used when considering the number of positive and negative ranks and their values.
Cliff