Classical logic and study design

Background:
The scientific value of a  study is determined by various factors, but to a major extent by the design of a study too.  
Methods:
Ex post, it is difficult to correct errors in study design completely.  Therefore, various mathematical aspects of a design of a study are discussed in this article.
Results:
Under conditions of causal investigations, it is appropriate to assure a study design with p(IOI) = 0.
The relative risk is refuted. The Odds ratio is refuted.
Conclusion:
A study of causal relationships properly planned should comply with p(IOI) = 0 as much as possible.