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J Clin Epidemiol. 2008 Mar;61(3):301-7. doi: 10.1016/j.jclinepi.2007.07.007. Epub 2007 Nov 28.

New insights on the relation between untreated and treated outcomes for a given therapy effect model is not necessarily linear.

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  • 1Institute for Theoretical Medicine and CNRS UMR5558, RTH Laennec School of Medicine, rue Guillaume Paradin, 69008 Lyon, France.



A relation between the size of treatment efficacy and severity of the disease has been postulated and observed as linear for a few therapies. We have called this relation the effect model. Our objectives were to demonstrate that the relation is general and not necessarily linear.


We extend the number of observed effect model. Then we established three numerical models of treatment activity corresponding to the three modes of action we have identified. Using these models, we simulated the relation.


Empirical evidence confirms the effect model and suggests that it may be linear over a short range of event frequency. However, it provides an incomplete understanding of the phenomenon because of the inescapable limitations of data from randomized clinical trials. Numerical modeling and simulation show that the real effect model is likely to be more complicated. It is probably linear only in rare instances. The effect model is general. It depends on factors related to the individual, disease and outcome.


Contrarily to common, assumption, since the effect model is often curvilinear, the relative risk cannot be granted as constant. The effect model should be taken into account when discovering and developing new therapies, when making, health care policy decisions or adjusting clinical decisions to the patient risk profile.

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