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

To compare prospectively obtained symptom scores (pre-tests) with retrospective assessment (then-tests) in patients with newly diagnosed advanced prostate cancer. 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. 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. 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.