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Table 3 Inclusion of the data source as a variable in the analysis of heterogeneity of the included meta-analyses

From: Primary versus secondary source of data in observational studies and heterogeneity in meta-analyses of drug effects: a survey of major medical journals

Meta-analysis Subgroup/ sensitivity analysis Meta-regression analysis
Exposure-related variables Outcome-related variables Other variables Type of data source included Exposure-related variables Outcome-related variables Other variables Type of data source included
Weiss J [20]
Harms outcomes
. . . No . . . No
Bally M [21] Timing of exposure to NSAIDs, dosage and duration of treatment, concomitant drug treatment Comorbidities Alternative statistical model, reason for exclusion No . . . No
Sordo L [22] Time interval in and out of opioid substitution treatment . Alternative statistical model No Treatment provider, prevalence of opioid injection, average methadone dose . Mean age, percentage of men, location, percentage of inpatient induction, percentage loss to follow-up, midpoint follow-up period No
Tariq R [23] Type of gastric acid suppressant (PPI and H2B reported together, PPI alone, or H2B alone) Case definition (time interval of recurrence: within 60 days vs within 90 days), type of diagnostic assay used for Clostridium difficile infection Study design, study setting (inpatients vs outpatients), data adjustment No . . . No
Maruthur NM [24] Mode of therapy . . No . . . No
Paul S [25]
Primary outcome
. Chronic or resolved hepatitis B virus infection Tumor and chemotherapy subtype, alternative statistical model, quality of design No . . . No
Paul S [25]
Secondary outcomes
. . Alternative statistical model, quality of design No . . . No
Li L [26] Type of control, mode of therapy, individual drugs . Length of follow up, type of design No . . . No
Molnar AO [27] . . Type of design No . . . No
Ziff OJ [28]
Primary outcome
. . Data adjustment, population type No Difference between digoxin and control arms at baseline: Diabetes, hypertension, diuretics, anti-arrhythmic drugs . Summary bias score, baseline study level variable: Year of publication, age, sex, previous myocardial infarction No
Ziff OJ [28]
Secondary outcomes
. . . No . . . No
CGESOC [29] Duration of use in current and past users of hormone therapy, types of hormone therapy Tumour histology and malignant potential of the tumour Study design, geographical region, age at first use of hormone therapy, age at menarche, parity, oral contraceptive use, height, bosy mass index, alcohol use, tobacco use, mother or sister with ovarian/breast cancer, histerectomy No . . . No
Bellemain-Appaix A [30] Clopidogrel dose Types of percutaneous coronary intervention Type of design No . . . No
Grigoriadis S [31] Timing of exposure to SSRIs . Study design, congenital malformations, control, meconium aspiration No . . . No
Li L [32] Type of incretin agents, type of control, mode of therapy, individual incretin agents . Length of follow-up, alternative effect measure, alternative statistical model No . . . No
Kalil AC [33] Different MIC cutoffs, assay type Hospital or 30-d mortality Publication year, quality of design No Vancomycin MIC cut-off, vancomycin exposure in the previous 6 months, vancomycin trough levels, proportion of patients who received vancomycin treatment Control mortality, APACHE II score, Charlson score, duration of bacteremia, proportion of patients with endocarditis, proportion of patients located in the intensive care unit Age No
Stegeman BH [34] Generation of progestogen used in combined oral contraceptives, combined oral contraceptive pill Method of diagnosis confirmation Funding source, study design Yes (outcome) . . . No
Maneiro JR [35] Type of biologic agent, concomitant treatment (monotherapy vs combined therapy), prior use of TNF inhibitors Type of disease Length of follow-up, data quality, study design, level of evidence of studies No Type of biologic agent, prior use of TNF inhibitors,
method of measurement of antibodies, type of the anti-TNF monoclonal antibody
Type of disease, time of disease duration, time to assess response Age and sex of patients, number of participants, length of follow-up, data quality, study design, level of evidence of studies No
Hartling L [36]
Primary outcomes
Type of drug-comparison Type of scale for the assessment of symptoms and quality of life . No . . . No
Hartling L [36]
Secondary outcomes
. . . No . . . No
Hsu J [37] Individual drugs, dosage of antiviral, timing of treatment . Data adjustment, confirmed influenza, type of influenza A vs B, pandemic versus seasonal influenza, severity of influenza, age, pregnancy, baseline risk (e.g. immune-compromised), setting, funding conflict No . . . No
Caldeira D [38]
Incidence of pneumonia
. . Study design, previous stroke, heart failure, chronic kidney disease, non-Asian patients No . . . No
Caldeira D [38]
Pneumonia related mortality
. . Study design No . . . No
MacArthur GJ [39] Duration of exposure to opiate substitution treatment . Data adjustment, geographical region, site of recruitment, monetary incentives, percentage of female participants, percentage of individuals from ethnic minorities No Exposure to methadone maintenance treatment at baseline only . Inclusion only of studies at lower risk of bias, inclusion only of studies that measured an incidence rate ratio, exclusion of studies that did not adjust for confounders No
Mantha S [40] Route of administration . Data adjustment No . . . No
Silvain J [41] Route of administration . Types of percutaneous coronary intervention, study publication, study size, quality of design No . . . No
McKnight RF [42] . . . No . . . No
  1. Abbreviations: APACHE acute physiology and chronic health evaluation, MIC minimum inhibitory concentration, SSRIs selective serotonin reuptake inhibitors, TNF tumor necrosis factor