A hypothesis about Spiegel et al.'s 1989 paper on Psychosocial intervention and breast cancer survival

In a randomized prospective study of 86 metastatic breast cancer patients by Spiegel et al. in 1989, the 50 who took part in a group psychosocial intervention survived on average 18 months longer than the 36 controls who did not. Because the control survival curve looked unusually steep, lacking an expected right-skewed tail, both curves were compared with that of a population from the same region having metastatic breast cancer. When transformed to life-table format, the curves of the control sample and the regional population, neither group having had an intervention, were almost identical for a year, and differed strikingly after 20 months. This led to the hypothesis that the 12 control patients surviving for more than 20 months were an extremely aberrant sample, being subject to the strong biasing influence of possible confounders, of which a considerable number are known, but not including those accounted for in the study. Corollaries to the hypothesis are that the intervention had no effect; that the intervention curve was in fact equivalent to a control curve with mild sampling departure from that of the regional population; and that, therefore, the repetition of the study now under way would not yield confirmation of the 1989 study, but rather, would support the hypothesis and the first two corollaries.