Metric for measuring Effectiveness of Prioritized Test Suite

For measuring how effective prioritized test suite is, we can use metric called APFD (Average Percentage of Faults Detected). The formula for APFD is given by :

APFD = 1 - ( (TF1 + TF2 + ....... + TFm) / nm ) + 1 / 2n

where, 
TFi = position of first Test case in Test suite T that exposes Fault i
m = total number of Faults exposed under T
n = total number of Test cases in T 

AFPD value can range from 0 to 100. The higher APFD value, faster faults detection rate. So simply put, APFD indicates of how quickly test suite can identify faults or bugs in software. If test suite can detect faults quickly, then it is considered to be more effective and reliable.

As the name suggests, test case prioritization refers to prioritizing test cases in the test suite based on different factors. Factors could be code coverage, risk/critical modules, functionality, features, etc.