Another more technical issue relates to a mismatch between certain published p-values indicating statistical significance and confidence intervals for mortality reductions indicating insignificance. "Statistics 101 says these two methods ought to agree," she says. To arrive at the findings reported in the Lancet, the investigators employed a complex statistical model for the cumulative incidence curves, undertaken only after they deemed the original method, a Cox proportional hazards model, to be suboptimal. According to Levin and Chiuzan, biostatisticians generally abhor this kind of post hoc methodological rejiggering. And it turns out the significant p-value referred to a different hypothesis than the one concerning mortality reduction.
The two biostatisticians say the UKCTOCS researchers deserve credit for organizing such a complex and ambitious study, and were suitably cautious in their reporting. Others have raised the possibility of financial bias in the Lancet paper: Ian J. Jacobs, one of two lead authors is also a co-inventor of ROCA and has a financial stake in its success. But Levin says in no way do the study's shortcomings rise to the level of fundamental errors of the kind he recently helped expose in the PACE trial for myalgic encephalomyelitis (a.k.a. chronic fatigue syndrome).
l problem was the overenthusiasm of the investigators with or without the financial impetus to put spin on the findings that should not yet be touted as life-saving," says Levin. "The bottom line is that the screening test is not ready for primetime. We need more evidence of a benefit."
The UKCTOCS study continues for another three years. Will additional data make a difference? We'll just have to wait and see. But according to the Mailman biostatisticians, the bar is always high for screening tests — particularly for a rare disease like ovarian cancer.
As any introductory biostatistics lecture makes clear, even if you have a screening test with 99 percent sensitivity and 99 percent specificity used in a population where one in a hundred people have the disease, you'll get a lot of false positives. "Half the time you'l scare the hell out of a patient and cause anxiety, stress, or other psychosocial consequences while they're not actually diseased," says Levin.
And this is better than the situation for ovarian cancer: while MMS did correctly identify substantially more cancers among those testing positive than did ultrasound alone, still, more than half of the positives were false positives. Says Levin, "That's why we need to be cautious."
The Abcodia statement about the test:
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