evidence-based medicine: systematic reviews
TRANSCRIPT
Evidence-Based
Medicine III:
Systematic ReviewsRAID 515
Rotation 6/2558
Nawanan Theera-AmpornpuntDepartment of Community Medicine
Faculty of Medicine
Ramathibodi Hospital
สไลด์บางส่วนดดัแปลงจากเอกสารประกอบการสอนของคณาจารย์ภาควิชาเวชศาสตร์ชุมชน คณะแพทยศาสตร์โรงพยาบาลรามาธิบดี มหาวิทยาลัยมหดิล
2
Recap of Previous EBM Lectures
Feedback on Last EBM Exercise (Risk & Harm)
Systematic Reviews
Lecture
Case & Paper Discussion
Critical Appraisal
Assignment
Outline
Recap of Previous
EBM Lectures
4
Steps in EBM
PICO
Survival & Survival Analysis
Censoring
Kaplan-Meier (Survival) Curve
Log Rank Test
Cox Regression (Cox Proportional Hazard Model)
Hazard Ratio
EBM: Prognosis
5
Risk & Harm
Types of Studies
RCTs & Cohort Studies
Case-Control Studies
Nested Case-Control Studies
Matched Case-Control Studies
Criteria for Causation
Odds Ratios
NNH & NNT
EBM: Risk & Harm
6
PICO & Search Keywords
Search Strategies
PubMed
PubMed Clinical Queries
PubMed MeSH Terms
OVID MEDLINE
Selecting Best Evidence
Critical Appraisals
EBM Skills
Feedback on Last
EBM Exercise
8
PICO: Question structure
Example:
P: Are patients with pain symptoms
I: who take conventional NSAIDs,
C: compared to those who take selective NSAIDs,
O: at an increased risk of peptic ulcer or GI bleeding?
EBM Exercise Feedback
9
PICO Question: Not too specific, but not too broad
Focus on patient population similar to this patient, but not exactly this patient
Pertinent features in PICO Question should be part of keywords
Selecting paper that best fits the question & your critical appraisal reveals good (valid, important & applicable) evidence
EBM Exercise Feedback
10
Avoid “Free full text” filter or limit
PubMed only shows those publicly available for free
PubMed doesn’t know which journals the university subscribes to (the ones that you can access full texts even though they ’re not free)
You could miss many relevant papers
EBM Exercise Feedback
11
Using OVID MEDLINE
Basic Search vs. Advanced Search
Advanced Search: Always put “AND” between words, otherwise will search for exact match
risk AND breast cancer AND contraceptive
EBM Exercise Feedback
Systematic Reviews
(Lecture)
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1.2.5.1 Identifying and selecting studies
1.2.5.2 Quality of evidence assessments
1.2.5.3 Combining the findings of independent studies
1.2.5.4 Variation between study findings
1.2.5.5 Summarizing and interpreting results
เกณฑ์แพทยสภาเรื่อง Systematic Reviews
http://www.tmc.or.th/file_08062012.pdf
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Types of Review Studies
http://www.docstoc.com/docs/126908275/Meta-analysis
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A clearly stated set of objectives with
pre-defined eligibility criteria for studies
An explicit, reproducible methodology
A systematic search that attempts to identify all
studies that would meet the eligibility criteria
An assessment of the validity of the findings of
the included studies, for example through the
assessment of risk of bias
A systematic presentation, and synthesis, of the
characteristics and findings of the included
studies
Key Characteristics of Systematic Reviews
http://handbook.cochrane.org/
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To collate all empirical evidence that fits pre-specified eligibility criteria in order to answer a specific research question
Uses explicit, systematic methods to minimize bias and provide reliable findings
Why Do Systematic Reviews?
http://handbook.cochrane.org/
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To provide more precise estimates of effects than estimates from individual studies, and increase power of statistical tests over individual studies, by combining information from all relevant studies
To facilitate investigations of consistency of evidence, and exploration of differences, across studies
Why Do Meta-Analyses?
http://handbook.cochrane.org/ http://en.wikipedia.org/wiki/Meta-analysis
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The power of a statistical test is
The probability that it correctly rejects the null hypothesis when the null hypothesis is false.
In other words, the ability of a test to detect an effect, if the effect actually exists.
Avoiding Type II errors (False-negatives)
Review: Statistical Power
http://en.wikipedia.org/wiki/Statistical_power
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เกณฑ์ 5 ข้อของแพทยสภาเป็นวิธีท า Systematic Reviews
1.2.5.1 Identifying and selecting studies
ค้นหาบทความและคัดเลือก1.2.5.2 Quality of evidence assessments
ประเมินคุณภาพของแต่ละบทความ1.2.5.3 Combining the findings of independent
studies
รวมข้อค้นพบจากแต่ละบทความ1.2.5.4 Variation between study findings
ความแตกต่างของข้อค้นพบระหว่างบทความ1.2.5.5 Summarizing and interpreting results
สรุปและแปลผลภาพรวมhttp://www.tmc.or.th/file_08062012.pdf
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Systematic review vs. Meta-analysis
Cochrane database of systematic reviews
Risk of bias in primary studies
Random effect vs. Fixed effect models
Heterogeneity (variation among studies)
Forest plot vs. Funnel plot
Keywords of Systematic Reviews
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1.2.5.1 Identifying and Selecting Studies
ค้นหาบทความและคัดเลือก
ค้นหาบทความในฐานข้อมูลต่างๆ เช่นMEDLINE: PUBMED
COCHRANE: reviews and database
EMBASE: Excerpta Medica Database
Grey Literature: thesis, dissertation, unpublished studies
ค้นหาอย่างน้อย 2 คนโดยเป็นอิสระต่อกัน น ามาคัดเลือกร่วมกันหรืออาจต้องมีบุคคลที่สามช่วยตัดสินในกรณีที่
ความเห็นไม่ตรงกัน
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1.2.5.2 Quality of Evidence Assessments
ประเมินคุณภาพของแต่ละบทความ
ตัวอย่างแนวทางการประเมินคุณภาพบทความ RCT
The Cochrane Risk of Bias Tool
Selection bias: allocation concealment
Performance bias: blinding participants & personnel (not always possible)
Detection bias: blinding assessors
Attrition bias: incomplete data due to withdrawals
Reporting bias: selective outcome reporting
Other biases: bias in other domains (e.g. carry-over effect in cross-over trials, contamination of intervention)
http://handbook.cochrane.org/
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1.2.5.3 Combining the Findings of
Independent Studies
รวมข้อค้นพบจากแต่ละบทความ
Meta-analysis: การประมวลผลรวมของการศึกษาต่างๆ เข้าด้วยกันด้วยวิธีการทางสถิติ มี 2 models
Fixed Effects Model
o Assumes that the true effect of treatment is the same for every study
Random Effects Model
o Assumes that the true effect estimate for each study varies
http://handbook.cochrane.org/
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1.2.5.4 Variation between Study Findings
ศึกษาความแตกต่างของข้อค้นพบระหว่างบทความ
Concepts and sources of heterogeneity
Clinical Heterogeneity: Differences in patients characteristics or treatment regimen (interventions)
Methodological Heterogeneity: Variation in study design, defining & measuring outcomes, duration of follow-up & other methodological factors (e.g. use of blinding & allocation concealment)
Statistical Heterogeneity (or Heterogeneity):Variability in intervention effects observed in different studies due to Clinical Heterogeneityand/or Methodological Heterogeneity
The Play of Chance: Random errors
http://handbook.cochrane.org/
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1.2.5.5 Summarizing and Interpreting Results
สรุปและแปลผลภาพรวม
http://handbook.cochrane.org/
Forest Plot
26http://handbook.cochrane.org/
Single True Effect among Studies (Fixed Effects)
Multiple True Effect among Studies (Random Effects)
Single vs. Multiple True Effects Among Studies
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Funnel Plot to Detect Publication Bias (“File Drawer Problem”)
http://handbook.cochrane.org/
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Funnel Plot: No Publication Bias Suspected
http://en.wikipedia.org/wiki/Meta-analysis/
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Funnel Plot: No Publication Bias Suspected
http://en.wikipedia.org/wiki/Meta-analysis/
Systematic Reviews
(Case &
Paper Discussion)
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Case Scenario & Search Strategy
แพทย์ปฏิบัติงานที่ โรงพยาบาลชุมชนแห่งหนึ่งพบผู้ป่วยชายอายุ 50 ปี เป็นเบาหวาน แต่ไม่เคยเป็นโรคหัวใจมาก่อน ถามว่า จะกินยาลดไขมันเพื่อป้องกันการเกิดโรคหัวใจได้หรือไม่
P Are patients with diabetes
I who take statin for primary prevention
C when compared to placebo
O at a decreased risk of cardiovascular diseases?
พิมพ์ search terms ใน PUBMED Clinical Queries ดังนี้diabetes statins "primary prevention"
"cardiovascular diseases" meta-analysis
พบ 7 บทความ ในคอลัมน์ Systematic Reviews
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Paper Selection
เลือกบทความชื่อStatins for primary prevention of cardiovascular and cerebrovascular events in diabetic patients without established cardiovascular diseases: a meta-analysis. Chen YH, Feng B, Chen ZW. Exp Clin EndocrinolDiabetes. 2012 Feb; 120(2):116-20
Systematic Reviews
(Critical Appraisal)
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Critical Appraisal Checklist for Systematic Reviews
What question (PICO) did the systematic review address?
Is it unlikely that important, relevant studies were missed?
Were the criteria used to select articles for inclusion appropriate?
Were the included studies sufficiently valid for the type of question asked?
Were the results similar from study to study?
What were the results?
Will the results help locally?
http://www.cebm.net/
Assignment
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Assignment
ไม่ต้องท าการบ้าน Systematic Review รายงาน EBM ฉบับสมบูรณ์ (เก็บคะแนน) เลือกท า 1 หัวข้อ จาก 3 หัวข้อ (ใช้ case เดิมได้) Prognosis Risk & Harm Systematic Review
ส่งเอกสารที่ธุรการภาควิชาเวชศาสตร์ชุมชน ภายในวันพฤหัสบดีที่ 29 ธ.ค. 2558 เวลา 16.30 น. (ส่งเฉพาะเอกสาร ไม่ต้องส่ง E-mail)