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What is the best evidence in medicine?
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What is the best evidence in medicine?

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Classification of evidences in the era of evidence-based medicine

Classification of evidences in the era of evidence-based medicine

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  • Interventional or experimental studyIs when the investigator tests whether modifying or changing something about the study participants alters the development or course of the outcome.Observational studies Involve the investigator collecting data on factors (exposures) associated with the occurrence or progression of the outcome of interest,without attempting to alter the exposure status of participants.The investigator does not intervene or manipulate the situation in any way, he or she simply observes.
  • Because past exposure information is collected retrospectively, case-control studies often rely on the subject’s recall of past events, which has the potential to lead to bias.
  • This study could be criticized for not quoting p value & C.I. but this was not normal practice at that time. This is a seminal paper & well worth a read.
  • Streptomycin and bed­rest (S case) or by bed­rest alone (C case).
  • Probably approaches 20.000/year
  • A sample of the population of interest is randomly allocated to one or another intervention and the two groups are followed up fora specified period of time. Apart from the interventions being compared, the two groups are treated and observed in anidentical manner. At the end of the study, the groups are analysed in terms of outcomes defined at the outset. The results from, say, the treatment A group are compared with results from the treatment B group. As the groups are treated identically apart from the intervention received, any differences in outcomes are attributed to the trial therapy.In paralel design: each group exposed only to one of study interventions.
  • Egger et al. (2003) have pointed out that the completeness of the literature search is an important feature of the meta-analysis to avoid publication bias or selection bias.
  • Publication & reporting biases:Positive results bias Grey Literature bias Time-lag bias Language & country bias Multiple publication bias Selective citation bias Database indexing bias Selective outcome reporting biasHealth Technology Assessment, 2000; 4(10):1-115
  • Pearls: لؤلؤةThe quality of most published information is very poor: Most published information is irrelevant and/or the methods are not good. Finding the high-quality evidence is like trying to sip pure water from a hose pumping dirty water, or looking for ‘rare pearls’.

What is the best evidence in medicine? What is the best evidence in medicine? Presentation Transcript

  • What is the best evidence?Samir Haffar M.D.Associate Professor of GastroenterologyAl-Mouassat University Hospital – Damascus – Syria
  • PatientvaluesClinicalExpertiseBest researchevidenceThe 3 components of EBP“EBM is the integration of best research evidencewith clinical expertise & patient values”- David SackettEBM
  • What is the best evidence?• The best evidence is the evidence most likely toprovide an unbiased view of the truth• Bias is difference between study results & truth• Of course, we can never know the truth, but we cantry to come as close as possible by performing &using well-designed & well executed studies View slide
  • Study typesInterventionalor experimentalRCTObservationalCase series & case reportCross-sectional studyCase-control studyCohort study View slide
  • Trial designs• Case report & case series &• Cross-sectional study• Case control study• Cohort study• Randomized clinical trialPrimary research• Systematic review• Meta-analysisSecondary research
  • Level of evidenceOxford Centre of EBMLevels ofevidenceBiasBiasBiasBiasBiasBiasValidity/StrengthofInferenceExpert opinionVCase-seriesIVIII Case-control studiesCohort studiesIIRandomized clinical trialsI bSystematic reviews (meta-analyses) of RCTsI a
  • Level of evidenceOxford Centre of EBMCase-seriesExpert opinionLevels ofevidenceBiasBiasBiasBiasBiasBiasValidity/StrengthofInferenceVIVIII Case-control studiesCohort studiesIIRandomized clinical trialsSystematic reviews (meta-analyses) of RCTsI bI a
  • Level of evidenceOxford Centre of EBMCase-seriesExpert opinionLevels ofevidenceBiasBiasBiasBiasBiasBiasValidity/StrengthofInferenceVIVIII Case-control studiesCohort studiesIIRandomized clinical trialsSystematic reviews (meta-analyses) of RCTsI bI a
  • Case report & case series• Case report describes medical history of a singlepatient in the form of a story• Case series is essentially the same of case report butwith more than one patient to illustrate an aspect of:- Condition- Treatment- Adverse reaction to tt (most commonly these days)* Rough search of MEDLINE database from 1997 to 200025% of published papers in clinical journals*
  • Thalidomide & limb defect• Classic example published in 1961 as a letter to theeditor by an obstetrician in Sydney• 3 newborn infants had same rare limb defect over 6 wkSuspected link between thalidomide & limb defect• > 10,000 affected children born worldwide before thisassociation confirmed & drug removed from the marketMcBride WG. Lancet 1961 ; 278 : 1358.
  • Level of evidenceOxford Centre of EBMCase-seriesExpert opinionLevels ofevidenceBiasBiasBiasBiasBiasBiasValidity/StrengthofInferenceVIVIII Case-control studiesCohort studiesIIRandomized clinical trialsSystematic reviews (meta-analyses) of RCTsI bI a
  • Case-control studyInvestigate etiology or outcome of diseasePetrie A, Sabin C. Medical statistics at a glance. Blackwell Publishing, 2nd ed, 2005.
  • Case-control study• AdvantagesQuick & cheap to performUseful for investigating rare diseases• DisadvantagesNot possible to calculate incidence & RRRetrospective: more prone to biasBest design in case of very low event rateMcGovern DPB et al. Key topics in evidence-based medicine.Bios Scientific Publishers, Oxford, UK, 1st Edition, 2001
  • Level of evidenceOxford Centre of EBMCase-seriesExpert opinionLevels ofevidenceBiasBiasBiasBiasBiasBiasValidity/StrengthofInferenceVIVIII Case-control studiesCohort studiesIIRandomized clinical trialsSystematic reviews (meta-analyses) of RCTsI bI a
  • Cohort studyInvestigate etiology or outcome of diseasePetrie A, Sabin C. Medical statistics at a glance. Blackwell Publishing, 2nd ed, 2005.
  • The world’s most famous cohort study• 34 440 British male doctors divided into 4 groups:Nonsmokers, light, moderate & heavy smokers• Publication of 20 year interim results in 1976Substantial excess in lung cancer mortality & all causemortality in smokers, with dose-response relationship• Publication of 40 year results: the same• Follow up: 94%BMJ 1976 ; 2 : 1525 – 1536.
  • Cohort study• AdvantagesProspective: less prone to biasIncidence, RR, & attributable risk calculatedEstimate of time from exposure to disease development• DisadvantagesTime consuming & costlyLong studies inevitably increases drop-out ratesNot useful for rare diseases (large number of subjects)McGovern DPB et al. Key topics in evidence-based medicine.Bios Scientific Publishers, Oxford, UK, 1st Edition, 2001
  • Case-control & cohort studies• Case-control & cohort studies are used to demonstrateassociation between suspected causes & disease• Despite important differences between these 2 studies,many of the rules regarding design & interpretationof the results of the studies are applicable to bothMcGovern DPB et al. Key topics in evidence-based medicine.Bios Scientific Publishers, Oxford, UK, 1st Edition, 2001
  • Level of evidenceOxford Centre of EBMCase-seriesExpert opinionLevels ofevidenceBiasBiasBiasBiasBiasBiasValidity/StrengthofInferenceVIVIII Case-control studiesCohort studiesIIRandomized clinical trialsSystematic reviews (meta-analyses) of RCTsI bI a
  • Perhaps the first large-scale clinical trial usinga properly designed randomized schema
  • Sir Austin Bradford Hill (1897 – 1991)British epidemiologist & statisticianThe father of modern RCTs
  • Number of RCTs per yearGlasziou P, Del Mar C. Evidence based practice workbook.Blackwell Publishing, 2nd edition, 2007.≈ 20,000 trials published each year> 500,000 trials in total
  • Basic structure of a RCT“gold standard” for assessing treatment effectsAkobeng AK. Arch Dis Child 2005 ; 90 : 840 – 844.Parallel trial is the most frequently used design
  • Randomized controlled trial• Advantages Prospective: accurate collection of dataExperimental & control groupRandomizationBlinding/masking• Disadvantages Expensive (difficult to get funded)Large number of patientsProlonged follow-upUsually answer one question
  • Level of evidenceOxford Centre of EBMCase-seriesExpert opinionLevels ofevidenceBiasBiasBiasBiasBiasBiasValidity/StrengthofInferenceVIVIII Case-control studiesCohort studiesIIRandomized clinical trialsSystematic reviews (meta-analyses) of RCTsI bI a
  • Systematic review & meta-analysisSystematic reviews(SR)Meta-analyses(MA)MA may, or may not, include a SREgger M et all. Systematic reviews in health care: Meta-analysis in context.BMJ Publishing Group, London, 2nd edition, 2001.
  • Steps of meta-analysis Formulation of the problem to be addressed Data collection Data recording Data analysis Reporting the results (Forest plot in metanalysis)Researchers should write in advance a detailed protocol
  • Data collectionFinding all studies• Electronic searchInitial search PubMed – Cochrane ReviewOthers databases: EMBASE, CINAHLFurther search References of relevant reviewsFind terms you didn‟t use (MeSH*)Search again Snowballing• Supplementary searchHand searchWrite to researchers* MeSH: Medical Subject Headings in MEDLINE
  • Studies included in meta-analysisStudies reviewedGrayliteratureAll studies publishedAll studies conducted
  • Cochrane collaborationhttp://www.cochrane.orgDatabase available free online in many countries
  • Antibiotic prophylaxis & pancreatic necrosisBai Y et al. Am J Gastroenterol 2008 ; 103 : 104 – 110.Forest plot
  • Bai Y et al. Am J Gastroenterol 2008 ; 103 : 104 – 110.Antibiotic prophylaxis & pancreatic necrosisThe diamondShows the overall result of MA
  • Advantages of systematic review/meta-analysis• Tight methodology eliminates biasYield same results when repeated by other investigators• Pooling of data empowers the resultNarrower CI than in primary studies• Heterogeneity between primary studies identifies newsubjects of research
  • Systematic reviews/meta-analysesindexed in PubMed – 10 years
  • * Altman DG et al. Ann Intern Med 2001 ; 134 : 663 - 94.Improving quality of reportsConsolidatedStandards ofReporting TrialsRCTsCONSORT*Systematic review& meta analysisPRISMA***Preferred Items forSystematic Reviewsand Meta-analyses*** http://www.prisma-statement.org/Quality ofReporting ofMeta-analysesMeta-analysisQUOROM**** Moher D et al. Lancet 1999 ; 354 : 1896 - 900.
  • Question type & study designStudy DesignQuestionIntervention RCTIncidence & prognosis Cohort studyPrevalence Cross-sectional studyEtiology & risk factors Cohort or case-controlDiagnosis Cross-sectional studyIn each case, SR of all available studies better than individual study
  • All of these studies should be critically appraised
  • 50,000 articles/yrfrom 120 journals~3,000 articles/yrmeet critical appraisal& content criteria(94% noise reduction)McMaster PLUS project – First levelCritical appraisal filters Valid Ready for clinical attentionHealth Information Research Unit – McMaster University – Canada
  • High quality/relevant data – PearlsGlasziou P, Del Mar C. Evidence based practice workbook.Blackwell Publishing, 2nd edition, 2007.Finding high-quality evidence like searching for „rare pearls‟
  • High quality/relevant dataPearlsIf not valid No valueIf not relevant No value
  • Limitations of evidence• Evidence simply doesn‟t exist• Some of what is availableNot easily accessibleNot clinically relevantNot of good qualityNot applicable to your patientIt takes time to develop high quality evidence& more time to get it to publication
  • There can be overlap of evidence at any levelA well designed RCT can be more useful thanmediocre meta-analysis
  • Conclusion• Hierarchy of evidence serves to guide clinicians in anordered manner to the best available evidenceEvidence from case report becomes more significant incase of absence of higher evidence• There can be overlap of evidence at any levela well designed RCT more useful than a mediocre MA
  • Mc Graw Hill2008ReferencesBMJ Publishing Group2003Elsevier2009
  • Thank You