Table 1 RELEVANT REG quality assessment tool for observational research

Primary items

 1. Background

1.1. Clearly stated research question

 2. Design

2.1 Population defined

2.2. Comparison groups defined and justified

 3. Measures

3.1. (If relevant), exposure (e.g. treatment) is clearly defined

3.2. Primary outcomes defined

 4. Analysis

4.1. Potential confounders are addressed

4.2. Study groups are compared at baseline

 5. Results

5.1. Results are clearly presented for all primary and secondary endpoints as well as confounders

 6. Discussion/interpretation

6.1. Results consistent with known information or if not, an explanation is provided

6.2 The clinical relevance of the results is discussed

 7. Conflict of interests

7.1. Potential conflicts of interest, including study funding, are stated

Secondary items

 1. Background

1.1. The research is based on a review of the background literature (ideal standard is a systematic review)

 2. Design

2.1. Evidence of a priori design, e.g. protocol registration in a dedicated website

2.2 Population justified

2.3 The data source (or database), as described, contains adequate exposures (if relevant) and outcome variables to answer the research question

2.4 Setting justified

 3. Measures

3.1 Sample size/Power pre-specified

 4. Analysis

NO SECONDARY ITEMS

 5. Results

5.1. Flow chart explaining all exclusions and individuals screened or selected at each stage of defining the final sample

5.2. The authors describe the statistical uncertainty of their findings (e.g. p-values, confidence intervals)

5.3. The extent of missing data is reported

 6. Discussion/interpretation

6.1. Possible biases and/or confounding factors described

 7. Conflict of interests

NO SECONDARY ITEMS