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Biometrics. 1999 Jun;55(2):560-4.

Reduced sensitivity to hidden bias at upper quantiles in observational studies with dilated treatment effects.

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  • Department of Statistics, The Wharton School, University of Pennsylvania, Philadelphia 19104-6302, USA. rosenbaum@stat.wharton.upenn.edu


When a treatment has a dilated effect, with larger effects when responses are higher, there can be much less sensitivity to bias at upper quantiles than at lower quantiles; i.e., small, plausible hidden biases might explain the ostensible effect of the treatment for many subjects, and yet only quite large hidden biases could explain the effect on a few subjects having dramatically elevated responses. An example concerning kidney function of cadmium workers is discussed in detail. In that example, the treatment effect is far from additive: It is plausibly zero at the lower quartile of responses to control, and it is large and fairly insensitive to bias at the upper quartile.

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