Box.

Principal advantages and limitations of the two main approaches to measuring the patient interval

	Strengths	Limitations
Patient interview (or questionnaire) studies	Potentially highly accurate and detailedCan allow for detailed (‘in-depth’) appreciation of relevant symptoms and their time of onset.	Limited representativeness (generalisability)Patients dying soon after symptom onset/diagnosis and those ‘too ill to take part’ are unlikely to be included.
Studies of medical consultation records	High representativeness (generalisability)Information about all cancer patients can be included, even for those with poor prognosis/only short-term survival.	Potential limitations in completeness and accuracyRely on doctors appropriately eliciting the timing of symptom onset as part of history taking and accurately interpreting and recording this information. Patient interval information may be missing.