You can find full details of the test in the Column Means Tests (No Effective Base Weighting) section of the CTABLES section of the Algorithms document.
You can find that document here. It's a pdf, so you can download for reference.
ftp://public.dhe.ibm.com/software/analytics/spss/documentation/statistics/27.0/en/client/Manuals/IBM_SPSS_Statistics_Algorithms.pdf
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