Consumer Health Informatics, Mobile Health, and Social Media for Health: Part...
Evidence-Based Medicine: Systematic Reviews
1. Evidence-Based
Medicine III:
Systematic Reviews
RAID 515
Rotation 6/2558
Nawanan Theera-Ampornpunt
Department of Community Medicine
Faculty of Medicine
Ramathibodi Hospital
สไลด์บางส่วนดัดแปลงจากเอกสารประกอบการสอนของคณาจารย์ภาควิชาเวชศาสตร์ชุมชน คณะแพทยศาสตร์โรงพยาบาลรามาธิบดี มหาวิทยาลัยมหิดล
2. 2
Recap of Previous EBM Lectures
Feedback on Last EBM Exercise
(Risk & Harm)
Systematic Reviews
Lecture
Case & Paper Discussion
Critical Appraisal
Assignment
Outline
8. 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. 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. 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. 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
13. 13
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
14. 14
Types of Review Studies
http://www.docstoc.com/docs/126908275/Meta-analysis
15. 15
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/
16. 16
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/
17. 17
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
18. 18
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
19. 19
เกณฑ์ 5 ข้อของแพทยสภาเป็นวิธีทา
Systematic Reviews
1.2.5.1 Identifying and selecting studies
ค้นหาบทความและคัดเลือก
1.2.5.2 Quality of evidence assessments
ประเมินคุณภาพของแต่ละบทความ
1.2.5.3 Combining the findings of independent
studies
รวมข้อค้นพบจากแต่ละบทความ
1.2.5.4 Variation between study findings
ความแตกต่างของข้อค้นพบระหว่างบทความ
1.2.5.5 Summarizing and interpreting results
สรุปและแปลผลภาพรวม
http://www.tmc.or.th/file_08062012.pdf
20. 20
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
22. 22
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/
23. 23
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/
24. 24
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 Heterogeneity
and/or Methodological Heterogeneity
The Play of Chance: Random errors
http://handbook.cochrane.org/
31. 31
Case Scenario & Search Strategy
แพทย์ปฏิบัติงานที่โรงพยาบาลชุมชนแห่งหนึ่งพบผู้ป่วยชายอายุ 50 ปี เป็น
เบาหวาน แต่ไม่เคยเป็นโรคหัวใจมาก่อน ถามว่า จะกินยาลดไขมันเพื่อป้องกัน
การเกิดโรคหัวใจได้หรือไม่
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 ดังนี้
diabetes statins "primary prevention"
"cardiovascular diseases" meta-analysis
พบ 7 บทความ ในคอลัมน์ Systematic Reviews
32. 32
Paper Selection
เลือกบทความชื่อ
Statins 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 Endocrinol
Diabetes. 2012 Feb; 120(2):116-20
34. 34
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/