We know that  performance of a developer is measured based on a number of defects detected in developed and quality of codes. but for tester or quality assurance team we will measure their efficiency and performance on the basis of following:

1. Defects should not be injected into successive phase or stage :

If tester missed any bugs and catches it later on next phases, it called defect injection. The tester should ensure that all defects of stage 1 or first phase should be exposed in the same phase, it should not be moved to next phase of development.

Example:- Suppose we are working on an e-commerce application. In the first phase we work(tested)on registration, select the item and add an item to the cart functionality. In next phase, we are testing payment module and we got an issue from registration module and the user is unable to select an item from a list for a specific scenario then it means bugs of the first stage injected into the second stage. Now bug resolving cost will be high.

2. Zero rejection defects:
 
If the tester does not have complete knowledge about application functionality and requirements are not clear to him. due to this he can report invalid bugs. Invalid bugs can hamper the project by utilizing and wasting the developers time on the investigation.

3.QA effort variance:

0% effort variance is not possible because the actual effort will not be equal to planned effort. If Effort variance is exceeded range 1 to -20%  then we consider it as effort variance. So due to lack of effort quality of product hamper.

There are some other metrics that are used to evaluate QA:

•  Number of bugs found in production server
•  Developer to QA ratio should be 2.5:1 to  3:1
•  Number of bugs found per person per release
•  Number of test cases executed by QA
•  % of automated test cases executed per release.