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Hayat Bentouhami,1 Joost Weyler1,2 1Social Epidemiology and Health Policy, University of Antwerp, Wilrijk, Belgium; 2StatUa Statistics Centre, University of Antwerp, Edegem, BelgiumCorrespondence: Hayat Bentouhami, University of Antwerp, Social Epidemiology and Health Policy, Doornstraat 331, Wilrijk, 2610, Belgium, Tel +32 265 28 33, Email hayat.bentouhami@uantwerpen.beAbstract: Good research is driven by study design encompassing theoretical design, design of data collection and design of data processing. In epidemiological research, theoretical design is based on a functional relationship between the occurrence and determinants studied (occurrence function) and should also define that part of the theoretical population and the context to which the results pertain (domain). Both are essential for the design of data collection, the design of data processing and the interpretation of the study results and should be explicitly reported. In order to gain insight into the role of theoretical design in the entire research process before publication, it was decided to informally question the corresponding authors of a selection of 30 articles (20 most recent and 10 less recent) reporting on causal observational epidemiological studies on asthma and early life exposure to antibiotics. The objective was to appraise the perceived knowledgeability of theoretical design among the authors of the selected articles. Fifteen authors responded. Authors were asked to indicate their knowledgeability with the concepts of theoretical design, causal theory, confounding and effect modification on a 5-level Likert scale. Other questions were related to the theoretical design of their study. The vast majority of the authors perceived themselves to be moderately to extremely knowledgeable with confounding and effect modification. Perceived knowledgeability of theoretical design and causal theory was more diverse. When provided with options for an occurrence function, almost all authors indicated “current occurrence as a function of past exposure” for their study. Nevertheless, half of these authors conducted their study based on “future occurrence as a function of current exposure”. Even though the authors perceive themselves to be knowledgeable with theoretical design, this is not reflected in their articles. Theoretical design should be well known, implemented and explicitly reported.Keywords: theoretical design, study design, etiologic research, epidemiological research

Hayat Bentouhami, Lidia Casas, Joost Weyler University of Antwerp, Social Epidemiology and Health Policy, Wilrijk, 2610, BelgiumCorrespondence: Hayat BentouhamiUniversity of Antwerp, Social Epidemiology and Health Policy, Doornstraat 331, Wilrijk, 2610, BelgiumTel +32 475 33 92 03Email hayat_bentouhami@hotmail.comAbstract: “Theoretical design” comprises the development of an occurrence relation and the specification of the study domain. In explanatory research, the occurrence relation causally relates one determinant to the occurrence (of an event or a state) taking into account other relevant characteristics (confounders and modifiers). Conflicting results in explanatory research might be (partially) explained by differences in the “theoretical design” or by a mismatch between the “theoretical design” and the “design of data collection”. In this critical review, the reporting of “theoretical design” is assessed in articles on the association between early life antibiotic use and the occurrence of asthma. Articles investigating a relationship between early life antibiotic use and the occurrence of asthma were searched in PubMed and systematically selected for critical review. The full text was read and important elements of study design were extracted (the research question/hypothesis, seven key elements of “theoretical design” (measure of occurrence, case (event or state) definition, conceptualization (and operationalization) of the exposure, temporal relation between outcome and exposure, confounders and effect modifiers taken into account and the domain of the study), the method of data collection and the method of data processing). A comparison was made between articles published before and after the publication of the “Strengthening the Reporting of Observational Studies in Epidemiology” (STROBE) statement (2007). Sixty-three articles were included for review. Thirteen articles reported the seven key elements of “theoretical design” that were questioned. No marked differences in reporting were observed pre- and post-STROBE. All articles reported some key elements of “theoretical design”; however, the reporting is not structured and not linked to the concept of “theoretical design”. Conceptualizing, delineating and explicit reporting of “theoretical design” is quintessential for the quality and transparency of explanatory research.Keywords: theoretical study design, occurrence function, etiological research, antibiotic use, asthma