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Also known as “Standard Score”. The number of standard deviations by which the value of a raw score (i.e., an observed value or data point) is above or below the mean value of what is being observed or measured.  – Wikipedia

CRO Example

The very, overly, simple version: a statistical measure of the difference between test variation samples. The larger the Z-score, the more certain you can be about the reported improvement in test result data. Proper application of a bell curve visualization makes it easier to understand and interpret. Here’s some additional reading that goes more in-depth and explains it much more thoroughly:

Additional reading

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