Classification of Screening instruments: ECG will be Minnesota coded by two trained and independent coders, and discrepant reports will be resolved with a third independent coder. All cases of probable or possible CAD on Minnesota coding of ECG would be classified as “MC ECG positive for CAD” RQ will be coded according to standardized criteria into “positives for "angina" and "history of possible infarction" . Presence of either one would be classified as “RQ positive for CAD”.