Friday, September 14, 2012

The consequences of casual concepts of causation

Exposure to X-rays can cause cancer, so their use as a routine and repetitive screen for tuberculosis (and, for readers old enough to remember, to look for the fit of shoes at a shoe-store), or for routine CT scans, and so on, is questionable.  Dental x-rays seem to be so safe that their risk, which is probably not zero, is nearly unmeasurable and presumably worth the dental problems they can find (hopefully, though not certainly, they are not taken too often as a source of profit).

Developing breast tissue in young girls is vulnerable, so they were not routinely given chest x-rays.  But breast cancer is common and serious, so mammography was seen for a long time as clearly a valuable life-saver, if used on peri- or post-menopausal women.  But recent studies have raised questions.  Interestingly, this is not because of new cancers that may be caused by the screening (though the number may not be zero).  It was because they could detect small anomalies that were then followed up.   Some would turn out to be cancer, even if in an early stage.  But the follow-up is psychologically traumatic and has its own unexpected consequences.  And even more, studies have shown that some of these cancers would regress on their own.  So mammography, despite so many being convinced of its value, is now under scrutiny:  when and how often and on who is this false positive risk too great to justify routine mammographic screening?

PSA testing has become routine for finding prostate cancer in older men, because prostate cells that are too active churn out PSA (prostate specific antigen), so high PSA levels, just as with suggestive mammograms, have been considered indicative of the need for follow-up.  Again, that has its own morbidity--including, gulp, impotence!--so it, too has come under scrutiny.  Indeed, as with mammography, studies have shown that the intervention's risk and the fact that many of the tumors would regress, or would stay silent until some other cause took the poor guy away, suggests that routine PSA testing be stopped.

Now, a new report suggests the same thing for ovarian cancer screening.  The reasons are the same, and surely there will be as much controversy.   What is this all about, and what is one to do, and why do we see this?  Surely and hopefully, it cannot be all, or even primarily, due to the profitability of screening services and follow-up.

More likely this reflects the belief in technology, fed by and into the hunger for early diagnosis and treatment of very nasty diseases that threaten the quality of life or even life itself.  Is it that early ideas about what might be early risk factors, based on some first rounds of studies, lead researchers anxious for important findings, and clinicians anxious for effective detection, to believe what are not very sound results?  This must be the case, unless the early studies were seriously flawed in their methodology.

Probably more importantly, this reflects a profound modern-day problem in science: the way that complex, multi-factor causation is studied by statistical studies, and the difficulty of getting good enough samples, well-enough understood, to generate reliable results.  Plus, many factors are lifestyle-related, and they change over time.

But could these findings be a reflection of a point we often wonder about, and that applies to evolutionary reconstructions as well--namely, that the assumptions underlying statistical studies of these types make and test assumptions?  Is it that the methods assume a type or level of regularity that simply does not reflect how things really are?

If that is the case then we have to await the next brilliant insight that will transform  how we think.  Meanwhile, we are apparently stuck not knowing why results and opinion change so often, or whether we can trust the latest study more than the previous studies it overturns.....or whether we have to believe that the latest study, too, will shortly be overturned.

Either the situation is straightforward but we just haven't done the right studies, or we're in a deeper epistemological hole than most people would like to think, calling for the kinds of creative thinking that no grant or research 'system' can order up, but simply depend on the lucky arrival of the required genius.

1 comment:

Holly Dunsworth said...

Seems like maybe we need more understanding of how the body heals without medical treatment. (Or how the body appears to be diseased quite frequently when it's not!) But where would the money be for that! (to answer myself) Perhaps Pharma could be interested in methods for inducing or mocking these coping/ healing systems in people who don't mount those responses or a big enough ones and instead get sick.