Dartmouth research examines the value of cancer...( k for certain cancers when they decide ...),Health

He and his colleagues compared the two mortality groups in 12 randomized studies of cancer screening for which both disease-specific and all-cause mortality could be determined. These trials involved screening for cancer of the breast, colon or lung.

In five of the 12 trials, the two mortality end points suggested opposite effects of screening. The researchers attributed these discrepancies to the two forms of bias that affect cause of death classifications. In one form, called sticky-diagnosis bias, deaths from other causes in the screened group are falsely attributed to cancer because that cancer was detected by screening. This type of misclassification influences the disease-specific mortality results against screening.

In the second form, called slippery-linkage bias, deaths from the screening process or subsequent treatment are falsely attributed to other causes. For example, if an invasive evaluation causes a patient to have a fatal heart attack, the death may be attributed to a heart attack rather than to the disease being tested for. This misclassification tilts the disease-specific mortality results in favor of screening.

Both forms of bias affected the randomized screening trials, according to the analysis, but the Dartmouth researchers argue that slippery-linkage bias had a larger effect. The concept of "slippery linkage" has been hinted at before but never previously defined, notes Black, who says he and his colleagues are among the first to investigate the impact of this bias.

Integrating both types of mortality classification can help avoid flaws in screening assessment, according to the researchers. They conclude that all-cause
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Contact: Hali Wickner
dms.communications@dartmouth.edu
603-650-1492
Dartmouth Medical School
5-Feb-2002