Prospective vs retrospective assessment of lower urinary tract symptoms in patients with advanced prostate cancer: the effect of 'response shift'.

OBJECTIVE: To compare prospectively obtained symptom scores (pre-tests) with retrospective assessment (then-tests) in patients with newly diagnosed advanced prostate cancer. PATIENTS AND METHODS: Patients with newly diagnosed locally advanced or metastatic prostate cancer were recruited. They completed the International Prostate Symptom Score (IPSS) and Symptom Problem Index (SPI) before starting treatment. At 3 and 6 months after diagnosis they again completed these questionnaires, but also retrospectively reassessed their initial symptom level. Healthy age-matched controls were recruited from primary care and completed the same questionnaires; in all, 76 patients and 17 controls participated.
RESULTS: The IPSS and SPI scores decreased significantly over the 6 months of the study. Patients retrospectively rated their level of symptoms and symptom bother as higher than their contemporaneous assessments. This was not the case in the control group.
CONCLUSION: These results question the assumption that contemporaneously collected pre-test scores are interchangeable with retrospectively assessed then-tests. This suggests that caution is required when comparing the results of studies that use these two alternative techniques of data collection. The difference between then-test and pre-test scores may represent an example of a phenomenon termed 'response shift', in which, by adapting to their disease, patients changed the internal standards by which they assessed their symptoms.