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This lecture includes these contents: How to read a systematic review, the fast tool, a systematic review, selective criticism of evidence, meta analysis plot, pros and cons of systematic reviews,... Invite you to consult this lecture.
How to read a Systematic Review: The FAST tool Find Appraise Synthesise Transferability Paul Glasziou Centre for Evidence Based Medicine University of Oxford www.cebm.net Are RCTs always needed for treatment questions? • Some immediate & dramatic effects don’t need RCTs* • Example: • Child with nasal foreign body Dislodged with Parent Kiss method Case series of success 15/19 o Botma J Laryngol Otol 2000 * Glasziou, Chalmers, Rawlins, McCulloch BMJ 2007 What you do? • For an acutely ill patient, you do a search • You find several studies: some show significant results but many others don’t Forest Plot/Blobbogram: of these 17 studies A B C D Which is the smallest study? Which is the largest study? How many are statistically significant? Which studies are “large enough”? Of these 17 studies: of streptokinase for MI How large should the study be? What sample size is needed? For disease X the usual mortality rate is 0% What sample size is needed to detect a reduction in mortality? • 100 • 1,000 • 100,000 • 1,000,000 Sample Size: Café Rule The 50:50 Rule (proportions) 50 events are needed in the control group: (For an 80% chance of finding a 50% reduction) Control Rate Number Events 20% 50 Control# Control# (Rule 1) (Fisher exact) 250 215 10% 50 500 463 5% 50 1000 962 Glasziou P, Doll H Was the study big enough? Two cafe rules Evid Based Med 2006;11(3):69-70 What sample size is needed? • There is usually a 12% mortality rate You think your treatment will lower mortality by 50% • What sample size is needed? What sample size is needed? • There is usually a 12% mortality rate You think your treatment will lower mortality by 50% • What sample size is needed? • 12% means 12/100 or 24/200 or 48/400 and 50 per 417 • Control + Treatment Groups = 834 in total Is the review any good? FAST appraisal • Question – What is the PICO? • Finding Did they find most studies? • Appraisal Did they select good ones? • Synthesis What to they all mean? • Transferability of results Combined results FIND APPRAISE SYNTHESISE TRANSFERABLE Using review results: what I with my patient? • STUDY: metaanalysis of behavioural interventions for insomnia adults “ confirms the efficacy of behavioral interventions for person with chronic insomnia.“ • PROBLEM: No regimens for ‘behavioural intervention’ described Author asked: “what specific treatment regime (or regimes) would you recommend based on your review?” Author response: “It was found that cognitive, behavioral and relaxation therapies all in general lead to similar improvements in sleep outcomesalthough cognitive approaches might have been a bit better. The references for these studies are found in the article. “ Rx “Behavioural Intervention” Summary: systematic reviews • Advantages Larger numbers & power Robustness across PICOs • Disadvantages May conclude small biases are real effects The results: Are studies similar? • What are the overall results? • Similarity of results Heterogeneity statistic • Similarity of question (PICO) Your judgement! Traditional cf systematic reviews • Traditional Many questions No search methods No inclusion criteria No combining studies • Systematic One question Explicit search Explicit inclusion criteria Combine study results (metaanalysis) Which are (i) statistically significant * and (ii) Clinically significant +? (a*+) (b+) (c*) Minimum clinical Important difference No difference (d) • Which studies (presented as Odds Ratio): Are not statistically significant? Have