Statistical sampling is a given as one of the tools and techniques for the PMI processes to plan quality management and control quality. It uses samples from the full population to estimate the situation of that population. For example, instead of detailed testing of every item coming off an assembly line, only a sample is tested. This can be useful when trying to identify the effect of a change.
Expertise in statistics is important to identify the size of the sample and to describe the strength of confidence in the result.
This technique is described in section 22.214.171.124 of the 5th edition of the PMBOK.