ANM Case 2 Research SRs (PDF)

SYSTEMATIC REVIEWS WEEK 2 ANM 150 Dr. Monique Aucoin ND MSc SOME HISTORY In 1987 Cochrane referred to a systematic review of corticosteroid treatment in pre-term births showed that a short-inexpensive course of corticosteroid treatment substantially reduced the risk of premature deaths due to...

SYSTEMATIC REVIEWS WEEK 2 ANM 150 Dr. Monique Aucoin ND MSc SOME HISTORY In 1987 Cochrane referred to a systematic review of corticosteroid treatment in pre-term births showed that a short-inexpensive course of corticosteroid treatment substantially reduced the risk of premature deaths due to complications Demonstrated that if a systematic review had been done 10 years earlier many premature deaths would have been avoided, & millions$ saved by avoiding duplicating/repeating RCTs OBJECTIVES Recognize the important features and strengths of a systematic review or meta-analysis Interpret an odds ratio and a forest plot Design a search strategy to find a systematic review on a topic LOOKING AT SYSTEMATIC REVIEWS Why do we do systematic reviews? As clinicians, why do we read them? What make a strong systematic review? METHODOLOGY Clear question? (think PICO!) Did they look for the right type of studies? -relevant to question, approp design (RCT if intervention) Comprehensive search? -databases, reference lists, unpublished studies, contact experts, non-English studies Clear eligibility criteria Assessment of individual study quality? RESULTS If results were combined, was it appropriate? -were the studies similar enough? - Or too much “heterogeneity”? HETEROGENEITY TEST Cochrane Q I2 Big question: Is the data too heterogeneous to combine and get a meaningful result? PUBLICATION BIAS Results of MA only valid if capturing the full range of trial results Vs all the negative studies ending up in a filing cabinet Attempt to analyze the potential for publication bias using the individual study data (magnitude of result, statistical significance) Plotted on a funnel plot - Look for symmetrical distribution FUNNEL PLOTS ASYMMETRICAL FUNNEL PLOTS COCHRANE COLLECTION The Cochrane Collaboration runs the Cochrane Library. Provides systematic reviews in a rigorous and consistent fashion Strong influence on policy – standards for practice Sections on complementary medicine (>70 reviews) Full access available through LRC website COCHRANE CAUTION Cochrane reviews are notoriously conservative in results. Frequently, it is concluded that ‘more research is necessary’. However, this is a reputable, non-biased source of reliable, up-to-date overview of evidence on a specific topic MINI STATS BREAK! More to come in week 10 – here’s a teaser! Statistical significance: Is there a REAL difference (between two numbers, two groups, multiple groups etc) or chance? Flipping a coin example. Is the difference because one is more likely or due to chance? 51 H/49 T → likely chance (H not more likely) 99 H/1 T → likely NOT due to chance (H is more likely) What about 70/30? A MORE RELEVANT EXAMPLE Study of 2 blood pressure drugs End of study BP is: Drug 1 – 133, Drug 2 – 129 Is drug 2 more effective? Or is the difference due to chance? What if the results were: Drug 1 – 133.7, Drug 2 – 133.9 We can’t tell! This is not enough information! STATISTICAL SIGNIFICANCE: P VALUE P-value -what are the odds that the difference is due to chance? -0.05 is generally the cut off (5% likelihood) -p greater than 0.05 → not significant -p less than 0.05 → significant Variables that influence this calculation: sample size, variation within the groups, variation between the groups More likely to detect significance: bigger sample, bigger difference between the groups STATISTICAL SIGNIFICANCE: CI 95% Confidence interval (CI) -we don’t know the exact result, if we repeated the experiment 100X, 95% of the time the results is within this range -if these intervals overlap → non-significant difference -if they don’t overall → significantly different STATISTICAL SIGNIFICANCE Ex 1. Systolic BP in treatment group 132.4 (95% CI 120.6-142.9), in control group 139.7 (95% CI 130.7-148.2) Significant? Ex 2. Systolic BP in treatment group 132.4, in control group 139.7 p=0.03 Significant? ODDS RATIO Looking at the relationship between an exposure (ex. Eating a food, taking a drug, exposure to a toxin) and an outcome (having a heart attack, a change in a blood value, being hospitalized) Often used in observational studies (but sometimes in clinical trials too) ODDS RATIOS OR = 1 exposure does not affect the likelihood of the outcome OR>1 exposure associated with increased likelihood of the outcome OR