ebm
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EBM. Dr. Nada AlYousefi April 25, 2012. Motivation: EBM “Successes”. Theophylline and asthma We were doing the wrong thing Littenberg, 1988 Beta blockers and MIs We weren’t doing the right thing Yusuf, 1987. Uses of “EBM”. Use of empirically-verified treatments in the care of patients - PowerPoint PPT PresentationTRANSCRIPT
EBMDr. Nada AlYousefiApril 25, 2012
Motivation: EBM “Successes”
•Theophylline and asthma▫We were doing the wrong thing
Littenberg, 1988
•Beta blockers and MIs▫We weren’t doing the right thing
Yusuf, 1987
Uses of “EBM”
•Use of empirically-verified treatments in the care of patients
•Incorporation of research results into the process of care
•Ability to critically appraise research results
What is Evidence-Based Medicine?
•“The integration of individual clinical expertise with the best available clinical evidence from systematic research.”
David L Sackett, W Scott Richardson, William Rosenberg, R Brian Haynes Evidence Based Medicine--How to Practice and Teach EBM, 1996
▫Various definitions
About 1/3 of worthwhile
evidence is eventually refuted
or attenuated
About 10% of published evidence
is worth reading
About 1/2 of relevant evidence is
not implemented
5 A’s
Steps of ebm
AppraisedAppraised TopicTopicTopicTopic::A subject of discussion or conversation
AppraiseAppraise::To evaluate, & estimate the quality, amountof validity, results and applicability
CriticalCritical::careful, exact evaluation and judgment
CriticallyCritically
“Best Available Clinical Evidence”•Therapy
▫Double-blind, placebo-controlled, randomized clinical trial
•Diagnosis▫Independent, blind comparison with a
reference standard•Prognosis
▫Representative and well-defined prospective cohort of patients at a similar point in the course of disease
•See Centre for Health Evidence
Levels of Evidences• (I-1) a well done systematic review of 2 or more
RCTs
• (I-2) a RCT
• (II-1) a cohort study
• (II-2) a case-control study
• (II-3) a dramatic uncontrolled experiment
• (III) respected authorities, expert committees, etc..
• (IV) ...someone once told me.... http://www.phru.org/casp/ See also AAFP
“Systematic Research”
•“Meta-analysis”
•“Literature synthesis”
▫From Michael Scriven
Questions
ARIF
Centre for EBM: http://163.1.212.5/docs/focusquest.html
Questions: PICO
Problems• Should a 30-year-old
woman with recurrent uncomplicated lower UTIs be advised to drink cranberry juice to prevent reinfection?
• For a 63 year old woman with Type 2 diabetes, is gabapentin superior to amitriptyline as first-line therapy for painful peripheral neuropathy?
Presentation will cover:• Relavance• PICO• search strategy• search results• the validity of this
evidence• the importance of
this valid evidence• can this valid,
important evidence be applied to your patient
Task•Well formulated question?•Formulate the query•Report back to us on your success•The whole group reports back in a week
Search for the Best Evidence
•Review articles•Community/professional standards•Systematic reviews•Original results
What are the Sources of Good Evidence?
www.welch.jhu.edu
http://ksu.edu.sa/Deanships/library/Pages/Home.aspxhttp://ksu.edu.sa/Deanships/library/Pages/Home.aspx
http://http://saudi.digitallibraryplus.comsaudi.digitallibraryplus.com
National Guideline Clearinghouse
www.guideline.gov
Website
CochraneWebsite
TRIP Database
www.tripdatabase.com(75 resources)…
Website
UpToDate
Website
Getting to PubMed
PubMed Response
PubMed Clinical Query
www4.ncbi.nlm.nih.gov/PubMed/
PubMed, Clinical Query, cont’d
Question
Context
Subject matter
Website
Controlled Vocabulary for Subject Matter
www.ncbi.nlm.nih.gov/pubmedwww.ncbi.nlm.nih.gov/pubmed
•Key concepts!•Auther
Stopwords
MeSH(The Medical Subject Headings )
Exercise
•Use the MeSH Database to build a strategy that will find citations to references discussing the economics of community-acquired pneumonia.
Exercise
•Use the NLM Catalog Journal search page to see if PubMed includes the journal, Molecular Microbiology. If so, retrieve all PubMed citations from this journal.
Exercise
•Use the Clinical Queries to find systematic reviews for accidents caused by sleep deprivation.
Search
•What role does pain have in sleep disorders?
Search
•To search for citations to articles written by Bonnie W. Ramsey about gene therapy for cystic fibrosis
Search
•To search for citations to articles about drosophila in the journal Molecular Biology of the Cell
Exercise
•Find citations to articles about the ethics of liver transplantation. Check Details to see how the terms are mapped. Filter to review articles. Select a few items and add them to the Clipboard. Go to the Clipboard and view the selected items in Abstract format to see the assigned MeSH terms.
Exercise
•Use the MeSH Database to build a strategy that will find citations to articles about schizophrenia resulting from prenatal exposure to influenza. Schizophrenia and influenza should be the major topics of the articles.
line Time
Types of Studies
Case ControlCase Control
Cross Cross SectionalSectional
Clinical TrialClinical Trial
Cohort studyCohort study
`Case SeriesCase Series
CaseReport
Types of Epidemiological Studies•Observational
Case Reports, Case series Cross - Sectional Case- Control Cohort
•Interventional Clinical Trials
Systematic review of RCTsSystematic review of RCTs
RCT
Cohort
Case control
InterventionalInterventional
ObservationaObservationall
validity
What’s A Paper on Therapy?•Clinical Trial (Controlled) Compares
INTERVENTION
with CONTROL
Clinical Trial Compares– INTERVENTION
Drug (New) Structured exercise program (e.g. osteoporosis) Surgical procedure
– CONTROL Placebo, old drug or old intervention Usual regular advise given (osteoporosis) Another surgical procedure / No surgery
Preparation: Randomization, Computer generated list
Eligibility assessment (Inclusion/exclusion) Consent Allocation to study arms (Concealment) Baseline assessment Initiation of intervention (Blind) Follow-up Outcome assessment Data analysis
process of RCTs
Appraise the Evidence• Assess validity? Correctness )likely
to be true(
• What are the results? Clinically
important
• Can we apply the results to our patient? Applicable in and useful for my patients
April 21, 2023
EBM
Jeddah Working
Group
64
VALIDITYRandomization.Concealment. Blindness. Follow up complete.Intention to treat.Similar groups at start.Both groups treated equally.
Randomization Randomisation = similar groups at
baseline Equal (50%) chance to be in either groupHow was it randomized?Was randomization concealed?
- selection- allocation
concealed allocation
Did investigators know to which group the potential subject would be assigned before enrolling them?
Trials with unconcealed allocation consistently overestimate benefit by ~40%
Selection bias
Reduced by: centralised randomisation on-site computer system with group
assignments in a locked file sequentially numbered, sealed, opaque
envelopes
Not: alternation, dates of birth, day of week.
BlindnessWho is Blind?
- Physicians-Nurses-Patients-Data gathering staff- data analyzers.
- Single, double…
Blindness•If patient knows: Placebo effect
Those who are on effective treatment perform better than those who receive Placebo
•If Physician knows: Overestimate Treatment effect (More care, Co-intervention)
Rx
C
Potential Subjects
Intervention starts
Outcome
Follow-up
• Selection bias • Performance bias
BlindnessConcealed Allocation
● duration of study.
● drop out < 20%.
All patients analyzed in the groups to which they were allocated
INTENTION TO TREAT (ITT)
200
100 100
50 70
3050
4040 IMPROVED
80%
OR
40%
57%
OR
40%
Drop out Drop out
intervention
control
Sources of bias in trials
Target population
Allocation
Selection bias
Performance bias
Attrition bias
Detection bias
Intervention Control
group(A) group
(B) Not exposed Exposed
Follow-up Follow-up
Outcomes Outcomes
Two balanced groups:
• Start Balanced: All prognostic factors are equally distributed at the start (Concealed Randomization)
• Run Balanced: All prognostic factors are maintained balanced throughout the study (Blindness and the 3C)
• End Balanced: All prognostic factors are maintained balanced at the end of the study (ITT)
Intervention
Therapy• ARR•RR
•RRR•NNT•CI
Result•Result Experimental Event Rate (EER)
Risk (or chance) of outcome event in experimental group
•Results control event rate (CER) Risk (or chance) of outcome event in
control group.
78
Result
Relative Risk (RR)•A measure of the chance of the event
occurring in the experimental group relative to it occurring in the control group.
•RR = EER / CER
79
•RRR=CER-EER/CER
•A RRR of 25% means that the new treatment reduced the risk of death by 25% relative to that occurring among control patients; the greater the relative risk reduction, the more effective the therapy.
Relative Risk Reduction (RRR ):.
•The absolute difference between the risk of the event in the control and experimental groups.
•ARR = CER – EER
Absolute Risk Reduction (ARR)
•Measure of clinical significance
•How many pat’s have to be treated with intervention in order one patient Would expected to benefit.
• NNT=1/ARR
•Conversely, can do number needed to harm▫uses harmful outcomes, eg death, weight gain
Number needed to treat (NNT)
Magnitude (treatment Magnitude (treatment effect)effect):
•Absolute effects (ARR & NNT)•Relative effects (RR, RRR )
Precision:Precision:oP value.P value.•Confidence interval?
Result Tabulation
Event Event
+ Ve+ VeEventEvent
- Ve- VeTotalTotal
ExperimentExperimental al
aabba+ba+b
ControlControlccddc+dc+d
•EER = Experimental Event Rate (a/a+b)
•CER = Control Event Rate (c/c+d)
BleedinBleedingg
presentpresent
BleedingBleeding
AbsentAbsentTotalTotal
Drug ADrug A 20208080100100Drug BDrug B40406060100100
•EER-A (Risk A) = 20/100 = 20% (0.2)•CER-B (Risk B) = 40/100 = 40% (0.4)
ARR = CER - EER
NNT = 1 / ARR
RR = EER/CER (Risk A/Risk B)
RRR = 1- RR
BleedinBleedingg
presentpresent
BleedingBleeding
AbsentAbsentTotalTotal
Drug ADrug A 20208080100100Drug BDrug B40406060100100
•ARR = CER - EER
NNT = 1 / ARR
•RR = EER/CER
RRR = 1- RR
ARR = CER – EER = 0.4 – 0.2 =
0.2 (20%)
NNT = 1 / ARR = 1/0.2 = 5
RR = EER/CER = 0.2/0.4 =
0.5
RRR = 1- RR = 1- 0.5=
0.5 (50%)
Confidence intervals?•The range within which the likelihood of a true value is expected to be within a given degree of certainty, usually evaluated at 95% CI.
•Precision
Summary•Validity - is the paper
likely to be true
•Importance - size of effect▫NNT ▫Percision
•Applicability - can it work for me/my setting
91