Total Number of Defects rejected/reopened by client after delivery. Or Defect leakage is the number of defects left uncovered after the test passes to next phase. It occurs at the client or end user side after the receipt of applications. After launching the application for the client, if the end user receives all kinds of defects using the application.
Defects missed from one level of testing to next level of testing is called defect leakage.
Unit level-> Component level ->Integration level -> System level -> Customer level -> End user level
Formula any level
Defect leakage = (No of defects found on the current
level/Total defects including the previous levels) *100
Example : System level defects found is 45 and the total
defects that include Unit level -> Component level -
>Integration level -> System level = 400
Then Defect leakage = (45/400)100 =11.25 percentage