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It seems like that the more is published on a single medical issue, the more it is difficult to obtain
a clear, logically consistent and comprehensive information on the given medical topic. This is one
of the reasons, why it is necessary to apply stringent standards and rigorous and strict study design
In spite of all the differences, the various types of studies have at least one thing in common: find
out, what is truth?
The impact of study design on necessary conditions and on sufficient conditions has been re-
investigated. The design of a study investigating necessary or sufficient condition should ensure as
much as possible, an index of unfairness as near as possible to 0.
Investigations of necessary or sufficient conditions require an index of unfairness equal to 0.