Table 3 Specification of purpose, objectives and scope

1.1.1 Commissioners of the overview

Whitlock 2008 [48,49,50,51,52]

1.1.2 Researcher or author team

Becker 2008 [1]; Whitlock 2008 [48,49,50,51,52]

1.1.3 Multiple/all stakeholders in collaboration

Caird 2015 [31]; Cooper 2012 [32]; Hartling 2012 [35]; JBI 2015 [40, 41]; Ryan 2009 [53, 54]; Whitlock 2008 [48,49,50,51,52]

Caird 2015 [31]; Hartling 2012 [35]

2.1.1 Map the type and quantity of available evidence (e.g. types of interventions, outcomes, populations/settings, study designs but not effects)

Becker 2008 [1]; Caird 2015 [31]; CMIMG 2012 [4]; Cooper 2012 [32]; Hartling 2014 [37]; Salanti 2011 [3]

2.1.2 Compare multiple interventions with the intent of drawing inferences about the comparative effectiveness of the interventions intervention for the same condition, problem or population

Becker 2008 [1]; CMIMG 2012 [4]; Cooper 2012 [32]; Hartling 2012 [35]; Hartling 2014 [37]; Ioannidis 2009 [38]; Ryan 2009 [53, 54]; Salanti 2011 [3]; Smith 2011 [57]

▪ An overview of interventions for nocturnal enuresis (Becker 2008 [1])

2.1.3 Summarise the effects of an intervention for the same condition, problem or population where different outcomes are addressed in different SRs

Becker 2008 [1]; CMIMG 2012 [4]; Cooper 2012 [32]; Hartling 2012 [35]; Hartling 2014 [37]; Ryan 2009 [53, 54]; Salanti 2011 [3]; Smith 2011 [57]

▪ An overview of hormone replacement therapy for menopause where outcomes may include bone density, menopausal symptoms, cardiovascular risk/ events, cognitive function etc. (Becker 2008 [1])

2.1.4 Summarise the effects of an intervention across conditions, problems or populations (e.g. “borrowing strength” when there is sparse data for a single condition and a similar mechanism of action for the intervention is predicted across conditions)

Becker 2008 [1]; Chen 2014 [2]; CMIMG 2012 [4]; Cooper 2012 [32]; Hartling 2012 [35]; Hartling 2014 [37]; Ryan 2009 [53, 54]; Salanti 2011 [3]; Smith 2011 [57]

▪ An overview of vitamin A for different populations and conditions (Becker 2008 [1])

2.1.5 Summarise unexpected (including adverse) effects of an intervention across conditions, problems or populations

Becker 2008 [1]; Chen 2014 [2]; CMIMG 2012 [4]; Cooper 2012 [32]; Hartling 2012 [35]; Ioannidis 2009 [38]; Salanti 2011 [3]; Smith 2011 [57]

▪ An overview of adverse effects of NSAIDs when used for osteoarthritis or rheumatoid arthritis or menorrhagia (Becker 2008 [1])

2.1.6 Identify and explore reasons for heterogeneity in the effects of an intervention (e.g. by examining reasons for discordant results or conclusions across SRs)

Bolland 2014 [30]; Caird 2015 [31]; Chen 2014 [2]; Cooper 2012 [32]; JBI 2015 [40, 41]; Singh 2012 [56]; Smith 2011 [57]

▪ Overview investigating differences between the meta-analyses of vitamin D for prevention of fracture (Bolland 2014 [30])

2.1.7 Other purposes

CMIMG 2012 [4]; Cooper 2012 [32]; Hartling 2014 [37]; JBI 2015 [40, 41]; Pieper 2012 [6, 45]; Robinson 2015 [48,49,50,51,52]; Ryan 2009 [53, 54]

2.2.1 Use a decision algorithm

Becker 2008 [1]; CMIMG 2012 [4]; Salanti 2011 [3]

▪ CMIMG editorial decision tree which covers decision points for choosing between an overview or a new or updated SR (with or without network meta-analysis) (Salanti 2011 [3])

2.2.2 Use other reasoning (triggers), for example, a new or updated SR might be more appropriate than an overview when SRs: (i) are not available, or have insufficient overlap with the overview question/PICO, (ii) have methodological shortcomings (including not being up-to-date), (iii) are discordant and the reason for discordance cannot be identified (e.g. by methodological differences), and (iv) need independent confirmation (or disconfirmation) (e.g. where SR authors have conflicts of interest such as industry ties or funding)

Chen 2014 [2]; Hartling 2014 [37]; Whitlock 2008 [48,49,50,51,52]; Singh 2012 [56]; Smith 2011 [57]

Caird 2015 [31]; Cooper 2012 [32]; Pieper 2012 [6, 45]; Smith 2011 [57]

2.4.1 Narrow scope-based on a well-defined question (specific PICOs) or methodological criteria restrictions (i.e. date range of eligible literature, sources searched, publication types and study designs, extent and quality of data extracted, type of synthesis undertaken)

Baker 2014 [29]; Chen 2014 [2]; CMIMG 2012 [4]; Cooper 2012 [32]; JBI 2015 [40, 41]; Pieper 2012 [6, 45]; Ryan 2009 [53, 54]; Salanti 2011 [3]; Thomson 2010 [58]

▪ Interventions restricted to a specific intervention for a specific condition/population (e.g. smoking cessation therapies for reducing harmful effects of smoking during pregnancy)

2.4.2 Broad scope - based on a broadly defined question with diverse and multiple PICOs elements, or no methodological restrictions

Baker 2014 [29]; Caird 2015 [31]; Chen 2014 [2]; CMIMG 2012 [4]; Cooper 2012 [32]; JBI 2015 [40, 41]; Pieper 2012 [6, 45]; Pieper 2014 [46]; Ryan 2009 [53, 54]; Salanti 2011 [3]; Smith 2011 [57]; Thomson 2010 [58]

▪ Interventions of broad policy relevance (e.g. any intervention to reduce the harmful effects of smoking, including cessation therapies, mass media, and pricing policies.)

Baker 2014 [29]; Becker 2008 [1]; Cooper 2012 [32]; Hartling 2012 [35]; JBI 2015 [40, 41]; Li 2012 [44]; Ryan 2009 [53, 54]; Smith 2011 [57]; Robinson 2015 [48,49,50,51,52]; Thomson 2010 [58]