When an electronic CRF is in use, data entry is carried out at the investigative site where the clinical trial is conducted by site staff that have been granted appropriate access to do so. When using a paper CRF the pages are entered by data entry operators. Best practice is for a first pass data entry to be completed followed by a second pass or verification step by an independent operator. People prefer to use a Double Entry Verification method to reduce data entry error. Using this method, all the data is first entered into a data file. Then the data is entered again and compared against the first data during the second data entry process. Discrepancies are brought to the attention of the data entry person and they are resolved in real time during data entry.

Double Entry Verification works only if data are entered in exactly the same order as the original data entry. When operating in the Double Entry Verification mode, each time a new record is displayed, the field data will appear blank even if that record was already verified.