Study design in medical research: part 2 of a series on the evaluation of scientific publications.
BACKGROUND
The scientific value and informativeness of a medical study are determined to a major extent by the study design. Errors in study design cannot be corrected afterwards. Various aspects of study design are discussed in this article.


METHODS
Six essential considerations in the planning and evaluation of medical research studies are presented and discussed in the light of selected scientific articles from the international literature as well as the authors' own scientific expertise with regard to study design.


RESULTS
The six main considerations for study design are the question to be answered, the study population, the unit of analysis, the type of study, the measuring technique, and the calculation of sample size.


CONCLUSIONS
This article is intended to give the reader guidance in evaluating the design of studies in medical research. This should enable the reader to categorize medical studies better and to assess their scientific quality more accurately.
Röhrig
Bernd
B
Institut für Medizinische Biometrie, Epidemiologie und Informatik (IMBEI), Johannes Gutenberg-Universität Mainz. Bernd.Roehrig@mdk-rlp.de
du Prel
Jean-Baptist
JB
Blettner
Maria
M
D035843:Biomedical Research / Q000145:classification* / Q000458:organization & administration*; D002986:Clinical Trials as Topic / Q000145:classification*; D055811:Journal Impact Factor; D010506:Periodicals as Topic; D012586:Science / Q000458:organization & administration*