Types of studies
Retrospective and prospective cohort studies, case series, case control, and cross-sectional survey studies will be included, irrespective of the blinding employed (for example, single-blinded or open). To be included, studies must compare study participants on at least one of the PROGRESS-Plus factors.
Types of participants
Adult patients over the age of 18 meeting the NIH criteria for bariatric surgery will be included, irrespective of geographical location. The NIH criteria for bariatric surgery include having: (1) a BMI ≥40 kg/m2 or (2) a BMI ≥35 kg/m2 with at least one significant weight-related comorbidity.
Types of intervention
The intervention must be a bariatric surgery that may include the following procedure types: Roux-en-Y gastric bypass, sleeve gastrectomy, adjustable gastric band, vertical banded gastroplasty, jejunoileal bypass, biliopancreatic diversion, duodenal switch, mini-gastric bypass, loop gastric bypass, gastric placation, gastric balloon, or scopinaro procedure. Both open and laparoscopic approaches will be considered.
Interventions may be either universally implemented or targeted to a specific risk group. The control group must be assigned to receive no intervention, standard care or assigned to a wait-list group.
The outcome of interest is the utilization of bariatric surgery. Two groups have been a priori defined as (1) patients who are eligible for bariatric surgery and receive the procedure, and (2) those who are eligible for bariatric surgery but do not receive the procedure.
The PROGRESS-PLUS sociodemographic factors will be used to explore the factors associated with bariatric surgery delivery. P lace of residence will be categorized by the geographical location of residence classified as urban, suburban and rural. R ace/ethnicity/culture will be defined by ethnicity with the following categories: British; Eastern European, Western European, Asian, South Asian, Black, Hispanic, Aboriginal, and Other. O ccupation will be categorized as being professional, skilled, unskilled and unemployed. G ender/sex will be categorized as being male or female. R eligion will be categorized as identifying with Christianity/Catholicism, Judaism, Islam and Other. E ducation will be categorized by the highest level of education attained (graduate; post-secondary, secondary and primary). S ocioeconomic status will be documented as median and interquartile range (IQR) household income and will be categorized into the following income categories: <$50,000, between 50,000 and $99,000, or ≥ $100,000. S ocial capital will be defined by family support as being full support, some support or no support. Plus factors will include age and health insurance. Age will be documented as mean interquartile range and categorized into the following age categories: 18 to 19 years, 20 to 39 years, 40 to 59 years, and 60+ years. Health insurance will be defined by the type of insurance, classified as being universal, private or none.
Studies will be indentified through the bibliographic databases of EMBASE, Medline (See Appendix 1 in Additional file1), and hand searching of journals, meeting abstracts, technical or research reports, monographs, doctoral dissertations, bibliographies of retrieved papers, and relevant web sites. In addition, unpublished studies and gray literature will be sought through internet searches with specific websites targeted, including:
Statistics Canada: http://www.statcan.gc.ca/start-debut-eng.html
Royal College of Physicians and Surgeons of Canada: http://www.royalcollege.ca/
Institute for Clinical Evaluative Sciences: http://www.ices.on.ca/index.html
Canadian Institute for Health Information: http://www.cihi.ca
American College of Surgeons: http://www.facs.org/
National Centre for Health Statistics: http://www.cdc.gov/nchs/
National Institutes of Health: http://www.nih.gov/
Agency for Healthcare Research and Quality: http://www.ahrq.gov/
Royal College of Surgeons of England: http://www.rcseng.ac.uk/
Health and Social Care Information Centre: http://www.hscic.gov.uk/
European Institute for Health Records: http://www.eurorec.org/
Royal Australasian College of Surgeons: http://www.surgeons.org/
Australian Institute for Health and Welfare: http://www.aihw.gov.au/
The search strategies will be developed by an experienced librarian and peer reviewed using Peer Review of Electronic Search Strategy (PRESS). The final search strategy will combine medical subject headings (MeSH terms) and appropriate wildcards. No publication language limit will be set during the database searches. A lower date limit of 1980 will be set as the availability of bariatric surgery prior to 1980 was not widespread.
Two research assistants will review the title, abstraction or description of all trials identified by the literature search. Those studies that aim to explore bariatric surgery among individuals over the age of 18 will be selected for full-text review to determine if they meet inclusion criteria. Any discrepancy will be resolved by a third person.
Two researchers will independently extract data from included studies on a prepared data collection form. The data abstraction form will be pilot tested on a random sample of studies to ensure high inter-rater agreement between reviewers. Extracted data will include: study characteristics; primary outcome results; patient risk factors, including BMI, smoking status, mental health status, quality of life, and physical activity level; and details of the surgical intervention. The presence or absence of the following comorbidities will be documented: hypertension, dyslipidemia, diabetes, coronary artery disease, cerebrovascular disease, depression, hypothyroidism, sleep apnea, gastroesophageal reflux, osteoarthrisits, and cholelithiasis.
Two researchers will independently assess the quality of all studies included for review. Any discrepancy will be resolved by a third reviewer. To quantify the degree of bias in the included studies, the Newcastle-Ottawa Scale (NOS) will be used. The NOS was developed for quality assessment of observational epidemiological studies (http://www.ohri.ca/programs/clinical_epidemiology/oxford.asp). The NOS has three categories within which risk of study bias can be determined: selection, comparability and outcome. In assessing risk of bias in cohort studies, the NOS awards a ranking for the selection of the cohort, comparability of the cohort and for the assessment of outcomes. In assessing risk of bias in case–control studies, the NOS awards a ranking for the selection of cases and controls, in the comparability of cases and controls and for the ascertainment of the exposure.
Data synthesis and analysis
Health inequities in accessing bariatric surgery will be explored using two of the following methods: first, data permitting, metaregression via a multivariate logistic regression using study-level data will be used to explore the PROGRESS-PLUS factors associated with the utilization of bariatric surgery (yes/no). This analysis will allow for the assessment of the impact of any individual covariates on utilization rates, as well as of a potential effect modifier. In addition, differences in PROGRESS-PLUS factors between the surgery and no surgery group within individual studies will be explored. The proportion of study participants categorized within each PROGRESS-PLUS category will be summarized as a percentage with a corresponding 95% confidence interval (CI) for dichotomous and categorical variables, and as median and interquartile range (IQR) for continuous variables. Second, differences in PROGRESS-PLUS factors between groups will be compared using χ2 test or Fisher’s exact test for categorical variables and the Wilcoxon-Mann–Whitney test for continuous variables. Statistical tests will be carried out as 2-tailed tests at α = 0.05. The DerSimonian and Laird method will be used to test heterogeneity of effect sizes between studies. Heterogeneity will be assumed at P <0.05 and I2 ≥25%. Data will be analyzed with SAS (version 9.1; SAS Institute Inc. Cary, NC, USA).
Irrespective of the presence or absence of heterogeneity the following subgroup analyses on the main outcome will be performed to explore possible effect modifications:
Intervention type; and