Item No | Recommendation | Where met and described, or if not met, reasons why not | |
---|---|---|---|
Title and abstract | 1 | (a) Indicate the study’s design with a commonly used term in the title or the abstract | See abstract first sentence ‘Methods’ section. |
(b) Provide in the abstract an informative and balanced summary of what was done and what was found | See abstract ‘Methods’, ‘Results’ and ‘Conclusion’ section. | ||
Introduction | |||
Background/rationale | 2 | Explain the scientific background and rationale for the investigation being reported | See paragraphs 1–3 from Background |
Objectives | 3 | State specific objectives, including any prespecified hypotheses | See last paragraph Background |
Methods | |||
Study design | 4 | Present key elements of study design early in the paper | See Methods paragraph 1 |
Setting | 5 | Describe the setting, locations, and relevant dates, including periods of recruitment, exposure, follow-up, and data collection | In Methods paragraph 1 and 2 the setting has been described as a Belgian national study based on data from TDI (1/1/2011–31/12/2014) and IMA (1/1/2008–31/12/2014). |
Participants | 6 | (a) Give the eligibility criteria, and the sources and methods of selection of participants | Methods paragraph 2 and 3 (cases): ‘As described in detail… 30,905 subjects were included in the study’ and 4 (comparators): ‘In addition a group of peers… matched to the 30,905 individuals in specialized treatment between 2011 and 2014.’ |
Variables | 7 | Clearly define all outcomes, exposures, predictors, potential confounders, and effect modifiers. Give diagnostic criteria, if applicable | See Methods paragraph 6 and 7 for the definition of the outcome (use and misuse of gabapentin): ‘The daily dose of gabapentin was calculated… The same method was used for people in treatment for substance use disorders as for people who had not been in specialized treatment.’ Given the cross-sectional data, age and gender are potential confounders, as well as region, as described in Methods paragraph 4. To adjust for these confounders the cases were matched to a group of comparators. There is little information available on potential confounders or effect modifiers other than these. The exposure (problematic substance use) was available in TDI for people with substance use disorders. As mentioned in Methods, third paragraph, for comparators, exclusion criteria for matching (excluding for problematic substance use) are mentioned in: Van Baelen L, De Ridder K, Antoine J, Gremeaux L: Longitudinal pharmacoepidemiological and health services research for substance users in treatment: protocol of the Belgian TDI-IMA linkage. Archives of Public Health, in press. |
Data sources/ measurement | 8* | For each variable of interest, give sources of data and details of methods of assessment (measurement). Describe comparability of assessment methods if there is more than one group | As described in Methods, paragraph 6, variables of interest and their source are given in Table 1. Details about all variables have been described in: Van Baelen L, De Ridder K, Antoine J, Gremeaux L: Longitudinal pharmacoepidemiological and health services research for substance users in treatment: protocol of the Belgian TDI-IMA linkage. Archives of Public Health, in press. |
Bias | 9 | Describe any efforts to address potential sources of bias | The potential confounding effect of age group, sex and region were taken into account when matching cases to comparators (Methods, fourth paragraph). Other sorts of bias are more difficult to address in this dataset, but we assess them in the Discussion. One source of bias could be the fact that 33% of patients with substance use disorders are registered without National Identification Number and its consequences for potential bias remain unknown (Methods, third paragraph). |
Study size | 10 | Explain how the study size was arrived at | The study size (numbers of cases, numbers of comparators) are straightforwardly derived from the TDI-database and the IMA-database. |
Quantitative variables | 11 | Explain how quantitative variables were handled in the analyses. If applicable, describe which groupings were chosen and why | The quantitative variables were used as available in both databases. No further manipulation was done, apart from the composite variable for use and misuse of gabapentin which is described in Methods paragraph 6: ‘The daily dose... The same method was used for people in treatment for substance use disorders as for people who had not been in specialized treatment.’ |
Statistical methods | 12 | (a) Describe all statistical methods, including those used to control for confounding | See Methods, last paragraph. |
(b) Describe any methods used to examine subgroups and interactions | Not applicable. | ||
(c) Explain how missing data were addressed | Data were only missing for descriptive variables. If data were missing for exposure or outcome variables (e.g. administrative errors), this information was not available. | ||
(d) If applicable, describe analytical methods taking account of sampling strategy | Not applicable. | ||
(e) Describe any sensitivity analyses | Not applicable. | ||
Results | |||
Participants | 13* | (a) Report numbers of individuals at each stage of study—eg numbers potentially eligible, examined for eligibility, confirmed eligible, included in the study, completing follow-up, and analysed | See Results, paragraph 1 and 2. |
(b) Give reasons for non-participation at each stage | Non-participation is not applicable, although some patients were registered without National Identification Number. This may cause bias, but no further information about potential direction is available. | ||
(c) Consider use of a flow diagram | Figure 1. | ||
Descriptive data | 14* | (a) Give characteristics of study participants (eg demographic, clinical, social) and information on exposures and potential confounders | Demographic characteristics are available in Table 3 and Appendix 1. |
(b) Indicate number of participants with missing data for each variable of interest | See Appendix 1. | ||
Outcome data | 15* | Report numbers of outcome events or summary measures | See Table 2 and Results paragraph 1 and 2. |
Main results | 16 | (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and their precision (eg, 95% confidence interval). Make clear which confounders were adjusted for and why they were included | See Table 3 and Results paragraph 3 and 4 |
(b) Report category boundaries when continuous variables were categorized | See Table 3; the only categorized continuous variable was age, but categories were predefined. For age, we combined existing categories (e.g.20–24 and 25–29) into one separate category (e.g. 20–29). Because of low prevalence figures above 20 for ‘number of prescriptions’ and ‘times of misuse’, we made one category. | ||
(c) If relevant, consider translating estimates of relative risk into absolute risk for a meaningful time period | Not applicable. | ||
Other analyses | 17 | Report other analyses done—eg analyses of subgroups and interactions, and sensitivity analyses | Not applicable. |
Discussion | |||
Key results | 18 | Summarise key results with reference to study objectives | This is the main focus of Discussion, paragraph 1 |
Limitations | 19 | Discuss limitations of the study, taking into account sources of potential bias or imprecision. Discuss both direction and magnitude of any potential bias | This is the main focus of Discussion, paragraph 4–6 |
Interpretation | 20 | Give a cautious overall interpretation of results considering objectives, limitations, multiplicity of analyses, results from similar studies, and other relevant evidence | This is the main focus of Discussion, paragraph 1–3 |
Generalisability | 21 | Discuss the generalisability (external validity) of the study results | This is the main focus of Conclusion |
Other information | |||
Funding | 22 | Give the source of funding and the role of the funders for the present study and, if applicable, for the original study on which the present article is based | This is the main focus of Funding |