About a type of bias in screening tests

The ostensible subject of this link is prostate cancer in families but it is not really the most important aspect. I feel the important aspect is the tendency of family members to be more intensely tested for a condition because a family member has been diagnosed with the condition. And then, because the extra testing finds evidence of most of the condition, the “experts” declare that there is a possible “genetic” cause while really what happened is that there has been extra testing.

It is a relatively subtle point but well worth the effort to understand. Additional, the author makes some excellent points about the way screening is done. Be sure to click through the links embedded within the article for much great in-depth information and analysis.

The excerpt below is from the Bioblog

Is prostate cancer common in families? It has been presumed to be so based on clusters of men in families that have been diagnosed with the disease. But in fact, it turns out that brothers of prostate cancer patients undergo more diagnostic activities – meaning it could be that they are diagnosed more simply because they are screened more.

It’s only natural – a first-degree relative gets a cancer diagnosis, and everyone in the family gets screened soon after for that cancer. It is encouraged by doctors because of the tendency for some cancers at least to have a clear genetic component. But the funny thing about prostate cancer is that similar to breast cancer, but even more so, the more you look for it the more you will find it. So a recent study tried to tease apart this cancer detection bias from a real genetic effect. Given that it is well understood now that a cancer diagnosis is a far, far different situation than having clinically significant (i.e. potentially harmful) cancer, they asked the pertinent question of whether or not prostate cancer clusters in families are due to genetics, or due to family members looking for it after a relative has been diagnosed. Apparently, in previous epidemiological studies, data simply for cancer rates have been used, without taking into account this potential bias…

much more via More Evidence That More Screening = More Cancer

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