Using data from existing EHR systems (rather than prospectively collecting new data explicitly for the trial) generally entails trading control for efficiency. That loss of control often involves some sacrifices, which are sometimes acceptable to the research team and sometimes unacceptable, depending on the study and its aims. To determine what trade-offs are acceptable for a given study, the investigator must begin with a very clear idea of the specific information needs for the trial (e.g. assess baseline characteristics) and then assess how much study integrity would be lost by using existing records data rather than attempting to collect new data. If using EHR data will support the data requirements for the study in a way that ensures integrity of the data and subsequent results, then researchers should take steps to ensure that possible errors, biases, and variation can be identified and minimized. As with any research study, and to be consistent with Good Clinical Practices for research, investigators should clearly define and collect only the “minimum necessary” data for the trial, and conduct quality assessments for all of the data being used, usually at multiple timepoints (for more on data quality reporting recommendations. Ultimately, as in all research, the scientific research question provides the foundation that will guide all decisions and activities of PCT research design and implementation, including the appropriate and optimal use of EHR systems and data.