Salmi et al proposed the attained effect (AE) and maximum attained effect (MAE) for an interventions. This appears to be a repackaging of the relative risk difference (see above), but with an emphasis placed on the ceiling effect for an intervention. The authors are from Universite Victor Segalen Bordeaux 2, Centre Hospitalier Universitaire, and McGill University in Montreal.


The ceiling effect is the maximum proportion of successes that one can expect for treating a condition under ideal conditions. The maximum ceiling effect (ideal therapy) is 1.


success rate for intervention A =

= 1 - (failure rate for A)


success rate for intervention B =

= 1 - (failure for B)


Values for the success rate range from 0 (no success) to 1 (100% success).


An assumption is that the outcome for intervention A is better than that seen with B.


attained effect =

= ((success rate for A) - (success rate for B)) / ((success rate for ceiling) - (success rate for B))


For the maximum attained effect (MAE) the success rate at ceiling is defined as 1.


If the MAE equation is rearranged using the failure rate then the equation becomes



= ((failure rate B) - (failure rate A)) / (failure rate for B)


which is the same equation as the relative risk difference multiple by -1. Ranges for MAE are from 0 to 1; ranges for RRD are from 0 to -1.



• Outcomes are considered either to be binary with either success or failure. All too often outcomes involve partial responses.


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