Facilitating meta-analyses by deriving relative effect and precision estimates for alternative comparisons from a set of estimates presented by exposure level or disease category.
ABSTRACT Epidemiological studies relating a particular exposure to a specified disease may present their results in a variety of ways. Often, results are presented as estimated odds ratios (or relative risks) and confidence intervals (CIs) for a number of categories of exposure, for example, by duration or level of exposure, compared with a single reference category, often the unexposed. For systematic literature review, and particularly meta-analysis, estimates for an alternative comparison of the categories, such as any exposure versus none, may be required. Obtaining these alternative comparisons is not straightforward, as the initial set of estimates is correlated. This paper describes a method for estimating these alternative comparisons based on the ideas originally put forward by Greenland and Longnecker, and provides implementations of the method, developed using Microsoft Excel and SAS. Examples of the method based on studies of smoking and cancer are given. The method also deals with results given by categories of disease (such as histological types of a cancer). The method allows the use of a more consistent comparison when summarizing published evidence, thus potentially improving the reliability of a meta-analysis.
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ABSTRACT: Studies suggest that vitamin D supplementation may reduce cancer and fracture risks. To examine the benefits and harms of vitamin D with or without calcium supplementation on clinical outcomes of cancer and fractures in adults. English-language studies identified from MEDLINE and the Cochrane Central Register of Controlled Trials through July 2011. Randomized, controlled trials (RCTs), prospective cohort studies, and nested case-control studies reporting incidence of or death from cancer and fracture outcomes. Multiple reviewers extracted details about participant characteristics, including baseline vitamin D status and use of supplements; details of statistical analyses, including adjustments for confounding; and methodological quality. Differences were resolved by consensus. 19 RCTs (3 for cancer and 16 for fracture outcomes) and 28 observational studies (for cancer outcomes) were analyzed. Limited data from RCTs suggested that high-dose (1000 IU/d) vitamin D supplementation can reduce the risk for total cancer, and data from observational studies suggested that higher blood 25-hydroxyvitamin D (25-[OH]D) concentrations might be associated with increased risk for cancer. Mixed-effects dose-response meta-analyses showed that each 10-nmol/L increase in blood 25-(OH)D concentration was associated with a 6% (95% CI, 3% to 9%) reduced risk for colorectal cancer but no statistically significant dose-response relationships for prostate and breast cancer. Random-effects model meta-analysis showed that combined vitamin D and calcium supplementation reduced fracture risk (pooled relative risk, 0.88 [CI, 0.78 to 0.99]) in older adults, but the effects differed according to study setting: institution (relative risk, 0.71 [CI, 0.57 to 0.89]) versus community-dwelling (relative risk, 0.89 [CI, 0.76 to 1.04]). One RCT showed adverse outcomes associated with supplementation, including increased risk for renal and urinary tract stones. Most trial participants were older (aged≥65 years) postmenopausal women. Observational studies were heterogeneous and were limited by potential confounders. Combined vitamin D and calcium supplementation can reduce fracture risk, but the effects may be smaller among community-dwelling older adults than among institutionalized elderly persons. Appropriate dose and dosing regimens, however, require further study. Evidence is not sufficiently robust to draw conclusions regarding the benefits or harms of vitamin D supplementation for the prevention of cancer. Agency for Healthcare Research and Quality.Annals of internal medicine 12/2011; 155(12):827-38. · 13.98 Impact Factor
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ABSTRACT: To systematically review and summarize the evidence of an association between preoperative smoking status and postoperative complications elaborated on complication type. The conclusions of studies examining the association between preoperative smoking and postoperative complications are inconsistent, thus there is a need for a review and meta-analysis to summarize the existing evidence. A systematic review and meta-analysis based on a search in MEDLINE, EMBASE, CINAHL, and PsycINFO. Included were original studies of the association between smoking status and postoperative complications occurring within 30 days of operation. In total, 9354 studies were identified and reviewed for eligibility and data were extracted. Forest plots and summarized relative risks (RR) including 95% confidence intervals (CIs) were estimated for various complication types. Of the 9354 identified studies, 107 studies were included in the meta-analyses and based on these, 157 data sets were extracted. Preoperative smoking was associated with an increased risk of various postoperative complications including general morbidity (RR = 1.52, 95% CI: 1.33-1.74), wound complications (RR = 2.15, 95% CI: 1.87-2.49), general infections (RR = 1.54, 95% CI: 1.32-1.79), pulmonary complications (RR = 1.73, 95% CI: 1.35-2.23), neurological complications (RR = 1.38, 95% CI: 1.01-1.88), and admission to intensive care unit (RR = 1.60, 95% CI: 1.14-2.25). Preoperative smoking status was not observed to be associated with postoperative mortality, cardiovascular complications, bleedings, anastomotic leakage, or allograft rejection. Preoperative smoking was found to be associated with an increased risk of the following postoperative complications: general morbidity, wound complications, general infections, pulmonary complications, neurological complications, and admission to the intensive care unit.Annals of surgery 06/2013; · 7.90 Impact Factor
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ABSTRACT: Previous epidemiologic studies have reported inconsistent results between parity and pancreatic cancer (PC) risk. To our knowledge, a comprehensive and quantitative assessment of this association has not been conducted. Relevant published studies of parity and PC were identified using MEDLINE (PubMed) and Web of Science databases until November 2013. Two authors (H-BG and LW) independently assessed eligibility and extracted data. Eleven prospective and 11 case-control studies reported relative risk (RR) estimates and 95% confidence intervals (CIs) of PC associated with parity. Fixed- and random-effects models were used to estimate the summary RR depending on the heterogeneity of effects. The summary RR for PC comparing the highest versus lowest parity was 0.86 (95% CI: 0.73-1.02; Q = 50.49, P<0.001, I2 = 58.4%). Significant inverse associations were also observed in the studies that adjusted for cigarette smoking (RR = 0.81; 95% CI: 0.68-0.98), Type 2 diabetes mellitus (RR = 0.83; 95% CI: 0.75-0.93), and those that included all confounders or important risk factors (RR = 0.85; 95% CI: 0.76-0.96). Additionally, in the dose-response analysis, the summary RR for per one live birth was 0.97 (95% CI: 0.94-1.01; Q = 62.83, P<0.001, I2 = 69.8%), which also indicated a borderline statistically significant inverse effect of parity on PC risk. No evidence of publication bias and significant heterogeneity between subgroups were detected by meta-regression analyses. In summary, these findings suggest that higher parity is associated with a decreased risk of PC. Future large consortia or pooled studies are warranted to fully adjust for potential confounders to confirm this association.PLoS ONE 01/2014; 9(3):e92738. · 3.53 Impact Factor