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This section describes the research design and methodology used in the six systematic reviews.

3.5.1 Systematic review research design

A systematic review seeks to collate all relevant evidence which meets a pre-specified eligibility criterion to answer a specific research question (Higgins and Green 2011). It uses specific, systematic methods to minimise bias in the identification, selection, synthesis, and summary of studies.

60 Systematic reviews are the preferred approach to synthesizing health care evidence due to holding methodological rigor (Moher et al. 2015). They have been used to support the development of clinical practice guidelines and inform clinical decision-making.

Moher et al (2015) outlines the key characteristics of a systematic review as being: (a) a clearly stated set of objectives with a clear, reproducible methodology; (b) a systematic search which identifies all studies meeting the eligibility criteria; (c) an assessment of the validity of the findings of all included studies (e.g. assessment of risk of bias and confidence in

cumulative estimates); and (d) systematic presentation and synthesis of findings from all included studies.

Meta-analysis uses statistical techniques to synthesise and summarise the results of included studies (Moher et al. 2009; 2015). This approach may or may not be used within a systematic review. It is advantageous in that by combining data from several included studies, it can provide precise estimates of the effects of health care than those derived from individual studies (Moher et al.2009; 2015).

The QUOROM Statement (Moher et al. 2000), was the reporting guidance for a meta-analysis of randomized trials (Moher et al. 2009). Since its application, the conduct and reporting of systematic reviews has changed considerably. Further, there have been many conceptual changes, including assessments of the risk of bias within systematic reviews (Guyatt et al. 2008), and the increasing use of systematic reviews to summarize evidence other than that provided by randomized trials (Moher et al. 2009). In an update and expansion of the statement, it was changed to the Preferred

61 Reporting Items for Systematic reviews and Meta-Analyses (PRISMA:

Moher et al. 2009).

The PRISMA Statement is an evidence-based minimum set of items for reporting in systematic reviews and meta-analyses, first published in 2009 (Moher et al. 2009). It entails a 27-item checklist (see Appendix 1) and a four-phase flow diagram. The PRISMA Statement aims to improve the reporting of systematic reviews and meta-analyses and even though primarily used for reporting reviews which evaluate randomized trials, it can be used for reporting systematic reviews of other research types (Moher et al. 2009).

There are alternative approaches to reporting a systematic review including those as suggested by Cochrane (Higgins and Green 2011), Campbell Collaborations and the Joanna Briggs Institute (Moher et al. 2015). The Institute of Medicine (IOM) also provides ‘Standards for Systematic Reviews’, but for reporting the review, “standards draw

extensively from the PRISMA checklist” (Institute of Medicine 2011). Thus,

the PRISMA Statement was the favoured approach for the reporting of the systematic reviews contained within this thesis.

3.5.2 Systematic review methodology

This study sought to identify peer-reviewed journal articles reporting longitudinal associations between PCRQ, school connectedness and adolescent use of alcohol, tobacco and cannabis. Six systematic reviews were undertaken, all reported in accordance with the PRISMA statement (Moher et al. 2009). This was to ensure literature was reviewed

systematically in addition to providing a robust evaluation of the evidence (Moher et al. 2009). The standardised methodology across all six

62 systematic reviews is detailed as follows, where methods needed tailoring for each individual review, it has been documented in the corresponding review:

Review design: Each review was designed and reported systematically,

according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement (see Appendix 1).

Electronic search: For each review, six electronic databases were searched:

Ovid Medline, PsycINFO (PI), ASSIA, ERIC, Web of Science and SCOPUS. The dates of the searches and the search terms used (see Appendix 2), were specific to each review.

Citation search: Additional papers were identified from citations of the

electronic search of included studies.

Exclusion criteria: All exclusion criteria were postulated prior to the search.

Within each review, papers were excluded if titles and/or abstracts

indicated that studies focused on study populations older than 18 years of age, multiple risk behaviours including teenage sexuality/pregnancy, or clinical or vulnerable (e.g. young offenders, attention deficit hyperactivity disorder and/or learning difficulties) populations. As were those not printed in English or cross sectional in design.

Exclusion criteria specific to each review were also formulated. This focused upon the population of interest, exposure and outcome for each review. This approach was based on the Cochrane ‘PICO’ statement (Higgins and Green 2011), which examines population of interest,

63 intervention, comparator and outcome, whereby the “I” for intervention is replaced with an “E” for exposure (PECO).

In addition to the exclusion criteria aforementioned, due to the longitudinal research design of this thesis, an important criterion of all reviews was that PCRQ or school connectedness preceded assessment of adolescent alcohol, tobacco or cannabis use. Studies not meeting this criterion were also excluded.

Abstract screening: Titles and abstracts were screened by one reviewer. Studies which raised uncertainty were discussed with two independent reviewers.

Screening of full papers: Full papers were read in detail and excluded

according to the criteria aforementioned. This process was individualised to each review. Results for each review were synthesised in EndNote.

Summary measures: Principal summary measures for all included studies

were odd’s ratios. Where this had not been reported, alternative summary measures were presented.

Quality assessment: For each review, all included studies were assessed for

methodological quality in accordance with a checklist derived from the Newcastle Ottawa Quality Assessment Scale (NOS: Wells et al. 2013) (see Appendix 3). The NOS is a convenient tool which has face/content validity (Wells et al. 2013). The NOS uses a 'star system' to assess the quality of cohort studies whereby each study is assessed against 8 specific criteria, across three domains: selection; comparability; and outcome. Criteria are rated as “yes” (*) or “no” (.).

64 All included studies were independently assessed against the NOS ‘star system’ by the main author. Scores were awarded, with a maximum possible score of 9. If >50% of the maximum score was obtained, the study was seen to be of high quality; if ≤50% of the maximum score was

obtained, then the study was seen to be poor quality and present

considerable risk for bias. This threshold was selected following a search on literature whereby a NOS score of less than 5 was considered “poor

quality” and likely to have biased or invalidated results (McPheeters et al. 2012). The quality assessment and associated NOS scores of all included studies has been presented within the results section of each of the six reviews.