Biases in electronic health record data due to processes within the healthcare system: retrospective observational study

Objective To evaluate on a large scale, across 272 common types of laboratory tests, the impact of healthcare processes on the predictive value of electronic health record (EHR) data. Design Retrospective observational study. Setting Two large hospitals in Boston, Massachusetts, with inpatient, emergency, and ambulatory care. Participants All 669 452 patients treated at the two hospitals over one year between 2005 and 2006. Main outcome measures The relative predictive accuracy of each laboratory test for three year survival, using the time of the day, day of the week, and ordering frequency of the test, compared to the value of the test result. Results The presence of a laboratory test order, regardless of any other information about the test result, has a significant association (P