Table 1.
Explanation on What Information Was Extracted and How This Information Was Extracted from the Articles
| Information Extracted | Explanation |
|---|---|
| 1. Journal | Needs no further explanation |
| 2. Year of publication | Needs no further explanation. |
| 3. Title of the article | Needs no further explanation. |
| 4. Aim of the study | The aim of the study reported at the end of the introduction section was copied. |
| 5. Research question or hypothesis of the study | The research question/hypothesis reported was copied. |
| 6. Whether the authors mentioned the word(s) “(study) design” in the text (including the location in the text) | Needs no further explanation. |
| 7. The case (event or state) definition for asthma | Needs no further explanation. |
| 8. Scientific T0 (and whether this was explicitly mentioned) and (theoretical) temporal aspects | T0 refers to scientific (reference) time. If the interest is in studying “future occurrence of asthma as a function of current exposure to antibiotics”, then the moment of realization of exposure is the reference (T0). If the interest is in studying the “current occurrence of asthma as a function of a history of antibiotic use”, then the moment of occurrence (asthma onset/diagnosis) is the reference (T0). If the T0 was not explicitly mentioned, a decision was made after discussion (HB and JW) on what T0 could have been after taking into account the aim or research question/hypothesis of the study, the measure of occurrence, the method of data collection, the method of data processing and the abstract (theoretical) temporal aspects of confounders. The following example refers to the process of defining T0: Aim: “ … to assess what the association is between the exposure to antibiotics in the first year of life and later risk on asthma occurrence by age 7.” Measure of occurrence: Future incidence Method of data collection: Longitudinal study Method of data processing: Cox proportional hazards regression Abstract temporal aspect of confounders: Confounders were assessed in the first year of life of the child T0 in this case would be at the age of 1 year. Incident cases of asthma would be detected from this point in time and onwards (= future occurrence). |
| 9. The measure of disease occurrence (eg: prevalence, incidence) and the abstract (theoretical) temporal aspect hereof (current-, future-)a | Needs no further explanation. |
| 10. The conceptualization of the exposure and the abstract (theoretical) temporal aspect hereof (past-, current-)a | The conceptualization of the exposure to antibiotics as reported by the authors was extracted. In case the exposure was conceptualized in multiple ways (eg antibiotic use during pregnancy, antibiotic use during the first year of life, …), all conceptualizations were extracted. Additionally the temporal aspect (past exposure to antibiotics if the interest was in the current occurrence of asthma or current exposure to antibiotics if the interest was in the future occurrence of asthma) was extracted from the article. |
| 11. The operationalization of the exposure | Operationalization of the exposure to antibiotics refers to how the authors operationalized exposure to antibiotics when the data were processed. This could be for example dichotomous (exposed vs non-exposed), but also in several categories of exposure (per class of antibiotic, per number of courses, …). |
| 12. The measurement method for the exposure | The method used to assess the exposure to antibiotics in the study was extracted. This can be for example a questionnaire. |
| 13. The measure of association | The estimate calculated by means of the statistical method applied to assess the strength of the association between antibiotic use and the occurrence of asthma was extracted from the article. This could be a hazard ratio, an odds ratio, an incidence density ratio, a causal fraction, …. |
| 14. Confounders taken into account (including the abstract (theoretical) temporal aspects) | All confounders taken into account and reported by the authors (including the timing of assessment) were extracted. |
| 15. Effect modifiers taken into account (including the abstract (theoretical) temporal aspects) | All effect modifiers taken into account and reported by the authors (including the timing of assessment) were extracted. |
| 16. The justification for the selection of confounders and/or effect modifiers | If any justification for the selection of confounders and/or effect modifiers (eg: selection based on a priori knowledge, selection based on the construction of a DAG,7 sufficient-component cause model8 …) was reported in the article, this was extracted. |
| 17. The domain of the study | The domain refers to the population to whom the results can be applied on.6 After reading the full text, the domain of the study reported (either explicitly or implicitly) was extracted. |
| 18. The design of data collection | The method used to collect the data for the study was extracted. This could be for example by means of a (birth) cohort, a case-control study, …. Example from a reviewed article: “The Home Allergens and Asthma Study is a prospective birth cohort study of children with a parental history of asthma or allergies in the Boston metropolitan area.” In this study the association between antibiotic use and the occurrence of asthma was assessed by using data from a prospective birth cohort. Therefore the design of data collection is a prospective birth cohort. |
| 19. The design of data processing | The main statistical methods used to process the data and to assess the association between antibiotic use and the occurrence of asthma was extracted from the article. |
| 20. Whether there is any referral to a methodological paper or work supporting the used methods or referral to a reporting guideline | If any referral was made to a methodological article, a theoretical work or a reporting guideline supporting the applied epidemiological methods in the study or the reporting, this was indicated with “yes”. |
Notes: aTemporal aspects refer to the time structure between the occurrence of asthma and the exposure to antibiotics. In etiologic research, a causal relationship between an outcome and an exposure can only be assessed when the exposure occurred before onset of the outcome under study; Italic font indicates text quoted from an article.