A brief skim of the study shows that the headline is a bit misleading. The correlation between coverage and bug yield is weak <i>when suite size is controlled for</i>.<p>Another way of looking at this is that large suites improve bug yield. They tend to have high coverage as a <i>by-product</i>, because a large test suite will hammer each unit from various directions.<p>My suspicion is that scoring coverage for <i>every</i> pass over an LOC or a pathway would change the result substantially.<p>Nothing in this paper is an argument that test coverage is useless; rather, it should be seen as a secondary metric that rapidly loses indicative value as it approaches 100%.<p><i>Number of test cases</i> seems to be the independent variable here.