3.3 Risk of bias within studies
Bias was mostly excluded from studies by the presence of DELC being measured without knowing the cardiac history shortly before undergoing angiography and with fairly consistent definitions of DELC and CAD. No patients were lost to attrition however two studies(4, 6) used non-cardiac patients as controls and it was assumed they had no CAD without undergoing angiography. Other potential biases are mentioned further in results.