This book introduces all common errors in medical science fields and the ways to control them. Systematic errors could be controlled both during study design and statistical analysis. Some errors have been presented in small segments but not in a comprehensive book. It covers many common errors that usually affect the research proposals, final reports, theses, and scientific presentations in the field of medical sciences as well as the rejection reasons on scientific papers. It will help researchers to control common errors using epidemiological and statistical methods.