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Introduction Due to the potential ethical issues associated with carrying out randomised controlled trials to investigate the impact of diagnostic delays on treatment and survival, the Clinical Practice Research Datalink (CPRD, formerly the GPRD) offers an alternative. This Trichostatin A (TSA) a large national database of electronic primary care medical records [, , ], which can be linked by NHS Digital  to Hospital Episode Statistics (HES), Office for National Statistics (ONS) mortality data and the Cancer Registry (CR). It is therefore possible to describe the patient pathway from presentation to long term follow-up . However, before robust statistical analysis can be carried out, it is necessary to ensure the accuracy of key clinical events such as cancer diagnosis . Using the linkage described above, it is now possible to investigate discrepancies between datasets, and whether these discrepancies can lead to significant differences in patient characteristics. Diagnoses recorded in CPRD are recorded either at the time of consultation or at a later date following hospital discharge or letters from clinics . Time-to-event studies rely on the diagnosis date. Differences in this date by database have not previously been clarified for individual cancers [7,8].
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