Exclusion criteria are not based upon methodological type but methodological quality.
First, there were slight methodological differences and exclusion criteria across the four cohorts analysed.
The first author extracted data from full texts into an Excel spreadsheet, comprising author, year, type of study, aim, population, participant age-group, methodological approach, methodology, inclusion and exclusion criteria, included and excluded participants, findings, limitations, conclusions, and directions for future research.
Methodological differences in subject recruitment, exclusion criteria, frequency and nature of procedures for follow-up, types of observations made, method of recording, methods of analysis and large intersite variability in some studies, make it difficult to evaluate the published data.
We extracted data including trial demographics (author, year of publication, country, funding source, publication status, duration of follow-up, number of centers involved, inclusion and exclusion criteria, and methodological quality using the Cochrane Collaboration Risk of Bias tool) [ 20, 21].
Articles were selected applying predefined inclusion and exclusion criteria and their methodological quality was graded according to the levels of evidence of the Oxford Centre for Evidence-Based Medicine.
Articles were selected by applying predefined inclusion and exclusion criteria, and their methodological quality was graded according to the levels of evidence of the Centre for Evidence-Based Medicine (Oxford, UK) [ 3].
Further details on inclusion and exclusion criteria and extracted clinical, methodological and statistical data can be found in the published protocols.
Review methods Search, application of inclusion and exclusion criteria, data extraction, and assessment of methodological quality, independently performed in duplicate.
The divergent results between the two studies might reflect methodological issues, such as sample sizes, ethnic differences, inclusion and exclusion criteria, or instruments to assess drug treatment response.
