3-day EBM workshop exercises€¦ · Web viewThe primary purpose of EBM sessions is to give you concrete experience in using searching and critical appraisal skills and in the context

Some of your sessions may be at the Old Road Campus (Churchill Hospital site) – so here is a map of how to get to the relevant buildings.

University of Oxford, 2009 1

Teaching Rooms

Evidence Based Medicine Thread Course Notes

TABLE OF CONTENTS

Topic Pages

Introduction 3

Program 4

Lecture: Introduction to Evidence Based Medicine 5Session 1: (A) Analysis of Asbtracts & (B) Critical Appraisal of a Therapy Study 8

Session 2: Systematic Rewiews & 15

Session 2: Asking questions & Library session 17

Session 3: Preparation instructions & 24

Session 3: Short Presentations 27

OTHER READINGS

Finding the Gold in Medline: clinical queries 29

Measures of Assocation 31

Measurement Scales 33

Sample Size Rules

Glossary


An introduction toEvidence Based Medicine

“Evidence-based medicine is the integration of best research evidence with clinical expertise and patient values” - Dave Sackett

Welcome to the evidence-based medicine theme. The primary purpose of EBM sessions is to give you concrete experience in using searching and critical appraisal skills and in the context of you current clinical learning and future practice. Our aim is to give you some basic skills that will be useful in your other medical terms (e.g., for writing up case reports) and for your own life long learning and future medical career.

At the end of this year you should be able to:

Recognise and formulate your own answerable clinical questions Identify the type of research that best answers the different classes of clinical

questions. Know which of several research databases (MEDLINE, Cochrane, Embase,

etc)and secondary resources (Clinical Evidence, Guidelines) are most likely to be helpful in answering different types of clinical questions.

Search using multiple text words and MeSH heading connected by Booleans (AND, OR, NOT) and truncations (* and $)

Appraise, and apply the results of different types of research studies to help in the management of individual patients. (Note: we will only cover therapy studies in detail; the other types – diagnosis, prognosis, aetiology - will be covered throughout the year).

Express the results of clinical trials in terms of both relative and absolute risk reductions, and be able to explain the numerical results to a patient.

Recommended TextStraus SE, Richardson WS, Glasziou PP, Haynes RB. Evidence-based Medicine: How to Practise and Teach EBM. Third Edition. Churchill Livingstone: Edinburgh, 2005 orBadenoch D, Heneghan C. Evidence-Based Medicine Toolkit, BMJ Publishing, 2002.

Also www.cebm.net - contains useful material, including a toolbox which has a glossary and useful breif summaries of the types of studies.

ContactDr Paul Glasziou Tel: 289298; email: [email protected]


EBM

http://www.cebm.net/

PROGRAMqThe program below will introduce you to the basics of Evidence-Based Medicine. During your terms in later years will include sessions on Evidence-Based Medicine and Evidence-Based Surgery. These will include sessions on diagnosis, on appraisal of surgical treatments, and further critically appraised topics of your own.

When? Where? What? Why?Thursday22nd October9:00-10:15

10:30-11:30

JR HospitalClassroom 7

Lecture/TutorialIntroduction to EBM & Analysis of Abstracts

Small Group tutorialCritical Appraisal of Trials

Introduction to the 4-step process of EBM (ask, search, appraise, & apply research evidence).

Practice of trial appraisal

Thursday 5th November9:00-10:15

10:30-11:30

JR HospitalClassroom 7

Lecture/TutorialAppraising Systematic Reviews

Searching Session

Introduction to systematic reviews and appraisal

Search & preparation for developing your own topic for January session.

To be announced

LectureDiagnostics

Presentation SessionPresentation of CATs (critically appraised topics)

Interpretation of diagnostic test information

Each Student will present for about 10 minutes on their topic of choice

November LectureIntroduction to Epidemiology(Adrian Smith)

Overview of study types

February Statistics Tutorial(Optional session)

Basic statistics plus answering any questions


Lecture slides here




Session ONE A: Analysis of AbstractsThis first session aims to familiarise you with the PICO structure of questions, and being able rapidly recognise these in research articles.

PART A. Exercise: study designs Read the abstracts from published studies on the following pages and answer the following questions for each study: 1. What is the question (PICO) of the study?2. What is the purpose of the study?

a. interventiona. frequency (incidence or prevalence) b. diagnostic accuracy c. prognosis (or natural history)d. aetiology and risk factors

3. Which study type would give the highest quality evidence to answer the question? (see ‘Levels of evidence table’) 4. Which is the best study type that is also feasible? (You can use the Table below as a guide)5. What is the study type used?

Table: levels of evidence according to type of research question Level

Intervention Diagnosis ** Prognosis Aetiology †††

I A systematic review of level II studies

Systematic review of level II studies

A systematic review of level II studies

A systematic review of level II studies

II A randomised controlled trial Cross-sectional study among consecutive presenting patients

A prospective inception cohort study

A prospective cohort study

III-1

A pseudo-randomised controlled trial (eg alternate allocation or some other method)

Cross-sectional study among non-consecutive patients

untreated control patients in a randomised controlled trial

A retrospective cohort study

III-2

A comparative study with concurrent control group: Nonrandomised

experimental study Cohort study, case-control

study, interrupted time series with a control group

Diagnostic case-control study

A retrospectively assembled cohort study

A case-control study

III-3

A comparative study without concurrent control group: Historical control study Comparison of two or more

single arm studies (ie case series from two studies)

Interrupted time series without a parallel control group

IV Case series Case series Case series, or cohort study of patients at different stages of disease

A cross-sectional study


Abstract 1 Voutilainen S, Rissanen TH, Virtanen J, Lakka TA, Salonen JT; Kuopio Ischemic Heart Disease Risk Factor Study. Low dietary folate intake is associated with an excess incidence of acute coronary events: The Kuopio Ischemic Heart Disease Risk Factor Study.

BACKGROUND: Although several prospective studies have shown that low folate intake and low circulating folate are associated with increased risk of coronary heart disease (CHD), the findings are inconsistent. METHODS AND RESULTS: We studied the associations of dietary intake of folate, vitamin B(6), and vitamin B(12) with the risk of acute coronary events in a prospective cohort study of 1980 Finnish men 42 to 60 years old examined in 1984 to 1989 in the Kuopio Ischemic Heart Disease Risk Factor Study. Nutrient intakes were assessed by 4-day food record. During an average follow-up time of 10 years, 199 acute coronary events occurred. In a Cox proportional hazards model adjusted for 21 conventional and nutritional CHD risk factors, men in the highest fifth of folate intake had a relative risk of acute coronary events of 0.45 (95% CI 0.25 to 0.81, P=0.008) compared with men in the lowest fifth. This association was stronger in nonsmokers and light alcohol users than in smokers and alcohol users. A high dietary intake of vitamin B(6) had no significant association and that of vitamin B(12) a weak association with a reduced risk of acute coronary events. CONCLUSIONS: The present work in CHD-free middle-aged men is the first prospective cohort study to observe a significant inverse association between quantitatively assessed moderate-to-high folate intakes and incidence of acute coronary events in men. Our findings provide further support in favor of a role of folate in the promotion of good cardiovascular health.

Question Answer1. What is the question (PICO) of the study? P

ICO

2. What is the purpose of the study? 3. Which study type would give the highest quality evidence to answer the question?4.Which is the best study type that is also feasible?5.What is the study type used?


Abstract 2 Lonn E, et al for the HOPE 2 Investigators. Homocysteine lowering with folic acid and B vitamins in vascular disease. N Engl J Med. 2006BACKGROUND: In observational studies, lower homocysteine levels are associated with lower rates of coronary heart disease and stroke. Folic acid and vitamins B6 and B12 lower homocysteine levels. We assessed whether supplementation reduced the risk of major cardiovascular events in patients with vascular disease. METHODS: We randomly assigned 5522 patients 55 years of age or older who had vascular disease or diabetes to daily treatment either with the combination of 2.5 mg of folic acid, 50 mg of vitamin B6, and 1 mg of vitamin B12 or with placebo for an average of five years. The primary outcome was a composite of death from cardiovascular causes, myocardial infarction, and stroke. RESULTS: Mean plasma homocysteine levels decreased by 2.4 micromol per liter (0.3 mg per liter) in the active-treatment group and increased by 0.8 micromol per liter (0.1 mg per liter) in the placebo group. Primary outcome events occurred in 519 patients (18.8 percent) assigned to active therapy and 547 (19.8 percent) assigned to placebo (relative risk, 0.95; 95 percent confidence interval, 0.84 to 1.07; P=0.41). As compared with placebo, active treatment did not significantly decrease the risk of death from cardiovascular causes (relative risk, 0.96; 95 percent confidence interval, 0.81 to 1.13), myocardial infarction (relative risk, 0.98; 95 percent confidence interval, 0.85 to 1.14), or any of the secondary outcomes. Fewer patients assigned to active treatment than to placebo had a stroke (relative risk, 0.75; 95 percent confidence interval, 0.59 to 0.97). More patients in the active-treatment group were hospitalized for unstable angina (relative risk, 1.24; 95 percent confidence interval, 1.04 to 1.49). CONCLUSIONS: Supplements combining folic acid and vitamins B6 and B12 did not reduce the risk of major cardiovascular events in patients with vascular disease.


ICO



Abstract 3 Chen SM, Chang MH, Du JC, Lin CC, Chen AC, Lee HC, Lau BH, Yang YJ, Wu TC, Chu CH, Lai MW, Chen HL; Taiwan Infant Stool Color Card Study Group, 2006. Screening for biliary atresia by infant stool color card in Taiwan. Pediatrics 117(4):1147–54. OBJECTIVE: We aimed to detect biliary atresia (BA) in early infancy to prevent additional liver damage because of the delay of referral and surgical treatment and to investigate the incidence rate of BA in Taiwan. METHODS: A pilot study to screen the stool color in infants for the early diagnosis of BA was undertaken from March 2002 to December 2003. We had designed an ‘infant stool color card’ with 7 numbers of different color pictures and attached it to the child health booklet. Parents were then asked to observe their infant's stool color by using this card. The medical staff would check the number that the parents chose according to their infant's stool color at 1 month of age during the health checkup and then send the card back to the stool color card registry center. RESULTS: The average return rate was approximately 65.2% (78,184 infants). A total of 29 infants were diagnosed as having BA, and 26 were screened out by stool color card before 60 days of age. The sensitivity, specificity, and positive predictive value were 89.7%, 99.9%, and 28.6%, respectively. Seventeen (58.6%) infants with BA received a Kasai operation within 60-day age period. The estimated incidence of BA in screened newborns was 3.7 of 10,000. CONCLUSIONS: The stool color card was a simple, efficient, and applicable mass screening method for early diagnosis and management of BA. The program can also help in estimating the incidence and creating a registry of these patients.


ICO



ession One B: Critical Appraisal of a Therapy StudyS

Scenario: A young woman presents having had a tick bite after walking in the New Forest 3 days ago. She removed most of the tick, and feels well but is concerned about developing Lyme disease which she has heard can be transimitted by ticks. She asks you if there is anything she should do?

What question(s) does this scenario raise? (try to PICO these)

Now work though the critical appraisal worksheets for the NEJM article, and:

decide what question (PICO) the study asked and answered

whether the internal validity of the study is sufficient to allow firm conclusions (all studies have some flaws; but are these flaws sufficient to discard the study?)

if the study is sufficiently valid, look at and interpret the results – what is the relevance or size of the effects of the intervention?

decide whether and how the results would apply to the original scenario or patient question.


THERAPY STUDY: Are the results of the trial valid? (Internal Validity)1. R- Was the assignment of patients to treatments randomised?

What is best? Where do I find the information?Centralised computer randomisation is ideal and often used in multi-centred trials. Smaller trials may use an independent person (e.g, the hospital pharmacy) to “police” the randomization.

The Methods should tell you how patients were allocated to groups and whether or not randomisation was concealed.

This paper: Yes No Unclear Comment:

2. R- Were the groups similar at the start of the trial?What is best? Where do I find the information?If the randomisation process worked (that is, achieved comparable groups) the groups should be similar. The more similar the groups the better it is. There should be some indication of whether differences between groups are statistically significant (ie. p values).

The Results should have a table of "Baseline Characteristics" comparing the randomized groups on a number of variables that could affect the outcome (ie. age, risk factors etc). If not, there may be a description of group similarity in the first paragraphs of the Results section.


3. A - Aside from the allocated treatment, were groups treated equally?

What is best? Where do I find the information?Apart from the intervention the patients in the different groups should be treated the same, eg., additional treatments or tests.

Look in the Methods section for the follow-up schedule, and permitted additional treatments, etc and in Results for actual use.


4. A - Were all patients who entered the trial accounted for? - and were they analysed in the groups to which they were randomised?

What is best? Where do I find the information?Losses to follow-up should be minimal - preferably less than 20%. However, if few patients have the outcome of interest, then even small losses to follow-up can bias the results. Patients should also be analysed in the groups to which they were randomised – ‘intention-to-treat analysis’.

The Results section should say how many patients were randomized (eg., Baseline Characteristics table) and how many patients were actually included in the analysis. You will need to read the results section to clarify the number and reason for losses to follow-up.


5. M - Were measures objective or were the patients and clinicians kept “blind” to which treatment was being received?

What is best? Where do I find the information?It is ideal if the study is ‘double-blinded’ – that is, both patients and investigators are unaware of treatment allocation. If the outcome is objective (eg., death) then blinding is less critical. If the outcome is subjective (eg., symptoms or function) then blinding of the outcome assessor is critical.

First, look in the Methods section to see if there is some mention of masking of treatments, eg., placebos with the same appearance or sham therapy. Second, the Methods section should describe how the outcome was assessed and whether the assessor/s were aware of the patients' treatment.



What were the results?6. How large was the treatment effect?

Most often results are presented as dichotomous outcomes (yes or not outcomes that happen or don't happen) and can include such outcomes as cancer recurrence, myocardial infarction and death. Consider a study in which 15% (0.15) of the control group died and 10% (0.10) of the treatment group died after 2 years of treatment. The results can be expressed in many ways as shown below.

What is the measure? What does it mean?Relative Risk (RR) = risk of the outcome in the treatment group / risk of the outcome in the control group.

The relative risk tells us how many times more likely it is that an event will occur in the treatment group relative to the control group. An RR of 1 means that there is no difference between the two groups thus, the treatment had no effect. An RR < 1 means that the treatment decreases the risk of the outcome. An RR > 1 means that the treatment increased the risk of the outcome.

In our example, the RR = 0.10/0.15 = 0.67 Since the RR < 1, the treatment decreases the risk of death.

Absolute Risk Reduction (ARR) = risk of the outcome in the control group - risk of the outcome in the treatment group. This is also known as the absolute risk difference.

The absolute risk reduction tells us the absolute difference in the rates of events between the two groups and gives an indication of the baseline risk and treatment effect. An ARR of 0 means that there is no difference between the two groups thus, the treatment had no effect.

In our example, the ARR = 0.15 - 0.10 = 0.05 or 5% The absolute benefit of treatment is a 5% reduction in the death rate.

Relative Risk Reduction (RRR) = absolute risk reduction / risk of the outcome in the control group. An alternative way to calculate the RRR is to subtract the RR from 1 (eg. RRR = 1 - RR)

The relative risk reduction is the complement of the RR and is probably the most commonly reported measure of treatment effects. It tells us the reduction in the rate of the outcome in the treatment group relative to that in the control group.

In our example, the RRR = 0.05/0.15 = 0.33 or 33%Or RRR = 1 - 0.67 = 0.33 or 33%

The treatment reduced the risk of death by 33% relative to that occurring in the control group.

Number Needed to Treat (NNT) = inverse of the ARR and is calculated as 1 / ARR.

The number needed to treat represents the number of patients we need to treat with the experimental therapy in order to prevent 1 bad outcome and incorporates the duration of treatment. Clinical significance can be determined to some extent by looking at the NNTs, but also by weighing the NNTs against any harms or adverse effects (NNHs) of therapy.

In our example, the NNT = 1/ 0.05 = 20 We would need to treat 20 people for 2 years in order to prevent 1 death.

7. How precise was the estimate of the treatment effect?The true risk of the outcome in the population is not known and the best we can do is estimate the true risk based on the sample of patients in the trial. This estimate is called the point estimate. We can gauge how close this estimate is to the true value by looking at the confidence intervals (CI) for each estimate. If the confidence interval is fairly narrow then we can be confident that our point estimate is a precise reflection of the population value. The confidence interval also provides us with information about the statistical significance of the result. If the value corresponding to no effect falls outside the 95% confidence interval then the result is statistically significant at the 0.05 level. If the confidence interval includes the value corresponding to no effect then the results are not statistically significant.

Will the results help me in caring for my patient? (ExternalValidity/Applicability)

The questions that you should ask before you decide to apply the results of the study to your patient are: Is my patient so different to those in the study that the results cannot apply? Is the treatment feasible in my setting? Will the potential benefits of treatment outweigh the potential harms of treatment for my patient?


Session TWO: Appraisal of Systematic Reviews

Case StudyA 55 year old man with known osteoarthritis presents because his pain is getting much worse. In particular the right knee is much worse than the left. Examination reveals some warmth, but no effusion. He is currently taking regular paracetamol and he cannot tolerate non-steroidal anit-inflammatories (NSAIDs) because of his past gastric ulceration. He asks if an injection is possible, as he has had friends who have had this. So you consider whether a corticosteriod injection* might be worthwhile.

Questions1. What are you clinical questions (PICOs)?

2. What sort of evidence would be helpful to answer the question(s)?

3. Where would you search for evidence and what terms would you use?

4. Now read and appraise the attached systematic review. How does their search compare to yours?


SYSTEMATIC REVIEW: Are the results of the review valid? What question (PICO) did the systematic review addressed?What is best? Where do I find the information?The main question being addressed should be clearly stated. The exposure, such as a therapy or diagnostic test, and the outcome(s) of interest will often be expressed in terms of a simple relationship.

The Title, Abstract or final paragraph of the Introduction should clearly state the question. If you still cannot ascertain what the focused question is after reading these sections, search for another paper!

This paper: Yes No Unclear Comment: F - Is it unlikely that important, relevant studies were missed? What is best? Where do I find the information?The starting point for comprehensive search for all relevant studies is the major bibliographic databases (e.g., Medline, Cochrane, EMBASE, etc) but should also include a search of reference lists from relevant studies, and contact with experts, particularly to inquire about unpublished studies. The search should not be limited to English language only. The search strategy should include both MESH terms and text words.

The Methods section should describe the search strategy, including the terms used, in some detail. The Results section will outline the number of titles and abstracts reviewed, the number of full-text studies retrieved, and the number of studies excluded together with the reasons for exclusion. This information may be presented in a figure or flow chart.

This paper: Yes No Unclear Comment:A - Were the criteria used to select articles for inclusion appropriate?What is best? Where do I find the information?The inclusion or exclusion of studies in a systematic review should be clearly defined a priori. The eligibility criteria used should specify the patients, interventions or exposures and outcomes of interest. In many cases the type of study design will also be a key component of the eligibility criteria.

The Methods section should describe in detail the inclusion and exclusion criteria. Normally, this will include the study design.

This paper: Yes No Unclear Comment:A - Were the included studies sufficiently valid for the type of question asked?What is best? Where do I find the information?The article should describe how the quality of each study was assessed using predetermined quality criteria appropriate to the type of clinical question (e.g., randomization, blinding and completeness of follow-up)

The Methods section should describe the assessment of quality and the criteria used. The Results section should provide information on the quality of the individual studies.

This paper: Yes No Unclear Comment:T - Were the results similar from study to study?What is best? Where do I find the information?Ideally, the results of the different studies should be similar or homogeneous. If heterogeneity exists the authors may estimate whether the differences are significant (chi-square test). Possible reasons for the heterogeneity should be explored.

The Results section should state whether the results are heterogeneous and discuss possible reasons. The forest plot should show the results of the chi-square test for heterogeneity and if discuss reasons for heterogeneity, if present.



What were the results?How are the results presented?A systematic review provides a summary of the data from the results of a number of individual studies. If the results of the individual studies are similar, a statistical method (called meta-analysis) is used to combine the results from the individual studies and an overall summary estimate is calculated. The meta-analysis gives weighted values to each of the individual studies according to their size. The individual results of the studies need to be expressed in a standard way, such as relative risk, odds ratio or mean difference between the groups. Results are traditionally displayed in a figure, like the one below, called a forest plot.

The forest plot depicted above represents a meta-analysis of 5 trials that assessed the effects of a hypothetical treatment on mortality. Individual studies are represented by a black square and a horizontal line, which corresponds to the point estimate and 95% confidence interval of the odds ratio. The size of the black square reflects the weight of the study in the meta-analysis. The solid vertical line corresponds to ‘no effect’ of treatment - an odds ratio of 1.0. When the confidence interval includes 1 it indicates that the result is not significant at conventional levels (P>0.05).

The diamond at the bottom represents the combined or pooled odds ratio of all 5 trials with its 95% confidence interval. In this case, it shows that the treatment reduces mortality by 34% (OR 0.66 95% CI 0.56 to 0.78). Notice that the diamond does not overlap the ‘no effect’ line (the confidence interval doesn’t include 1) so we can be assured that the pooled OR is statistically significant. The test for overall effect also indicates statistical significance (p<0.0001).

Exploring heterogeneity

Heterogeneity can be assessed using the “eyeball” test or more formally with statistical tests, such as the Cochran Q test. With the “eyeball” test one looks for overlap of the confidence intervals of the trials with the summary estimate. In the example above note that the dotted line running vertically through the combined odds ratio crosses the horizontal lines of all the individual studies indicating that the studies are homogenous. Heterogeneity can also be assessed using the Cochran chi-square (Cochran Q). If Cochran Q is statistically significant there is definite heterogeneity. If Cochran Q is not statistically significant but the ratio of Cochran Q and the degrees of freedom (Q/df) is > 1 there is possible heterogeneity. If Cochran Q is not statistically significant and Q/df is < 1 then heterogeneity is very unlikely. In the example above Q/df is <1 (0.92/4= 0.23) and the p-value is not significant (0.92) indicating no heterogeneity.

Note: The level of significance for Cochran Q is often set at 0.1 due to the low power of the test to detect heterogeneity.



ession Two(cont): Asking Questions & SearchingS

PART AIn this session you should try to formulate the questions for the scenarios provided and for one or more of your own scenarios (see the worked example on opposite page)

There are several supplied scenarios to choose from – do a couple of these.

There are also several blank scenario sheets for you own questions. You will need to do at least one of these (a patient you have seen, or a health problem of a relative, friend or even yourslef – please keep the identity confidential).

You should complete the upper half of the sheet (FORMULATE AN ANSWERABLE QUESTION), and begin the design of the search strategy in the lower half of the sheet (TRACK DOWN THE BEST EVIDENCE) – however, most of the search section you will complete in the next tutorial.


STEP 1: FORMULATE AN ANSWERABLE QUESTION

Example – Stockings for long flights?A 43 year old male asked for some repeat prescriptions and advice about preventing deep vein thrombosis on a 12 hour flight (his brother had had one last year). You suggest stockings as the most effective prevention.

QuestionPatient or Population: _ In patients on long flights ________________

Intervention or Indicator: __ do compression stockings __________________________

Comparator: ___ no compression stockings ___________________________________

Outcome: ____ prevent Deep Vein Thrombosis (DVT)___________________________

Question sentence: In patients on long flights(P), do compression stockings (I) prevent DVT (O)?

What type of question is this (phenomena, frequency, diagnosis, prediction, or intervention)?

What would be the ideal study type? (Randomised Trial, Inception cohort, Survey, etc)

What would be the best feasible study type?

STEP 2: TRACK DOWN THE BEST EVIDENCE

SEARCH STRATEGY DESIGN TABLEPrimary Term Synonym 1 Synonym 2

P ( flight* OR OR ) ANDI (stocking OR stockings OR ) ANDC ( OR OR ) ANDO (DVT OR thrombosis OR )

Note: consider truncation for each word and add an “*”, e.g., child* rather than children

ACTUAL SEARCHESCochrane Searches Hits PubMed Searches Hits

Key Reference: Scurr, Lancet 2000

Key Finding: __Grade I below knee compression stockings prevent most DVTs_________



Scenario 1– Beta-Blockers in Heart Failure?Over afternoon tea you a re discuss a patient with heart failure who had a myocardial infarction about 6 weeks ago. He has recovered well though: no breathlessness, pulse 80 regular, BP 136/85, chest is clear, but echocardiography shows reduced function with an LVEF (left ventricular ejection fraction) of 30% - which is well below normal. You wonder whether beta-blockers are safe and helpful in such a patient.

QuestionPatient or Population: _____________________________________________________________

Intervention or Indicator: ___________________________________________________________

Comparator: _____________________________________________________________________

Outcome: _______________________________________________________________________

Question sentence: ________________________________________________________________






P ( OR OR ) ANDI ( OR OR ) ANDC ( OR OR ) ANDO ( OR OR



Key Reference: ______________________________________________________________________

Key Finding: _________________________________________________________________________



Scenario 2 – Childhood Seizure RecurrenceChildhood seizures are common and frightening for the parents, and the decision to initiate treatment is a difficult one. What is the risk of further recurrences following a single seizure of unknown cause? Are there any identifiable factors that modify this risk?

QuestionPatient or Population: _____________________________________________________________


Comparator: _____________________________________________________________________

Outcome: _______________________________________________________________________










Key Reference: ______________________________________________________________________

Key Finding: _________________________________________________________________________



Your Scenario A

Your QuestionPatient or Population: _____________________________________________________________


Comparator: _____________________________________________________________________

Outcome: _______________________________________________________________________










Key Reference: ______________________________________________________________________

Key Finding: _________________________________________________________________________


Session Two (cont): Searching SessionFor your presentation you will need to do a search to find a study which helps to answer the question you formulated in the previous session.

Please note: during this session you will need to record the results of one search and your chosen article for the critically appraised topic you present later in the week.

You should use the second half of the sheets from Tutorial 1, viz.,


Use the ACTUAL SEARCHES tables for each of the questions to record the different terms you searched on, the number of hits, and the final “best evidence” you chose.

For intervention questions you should try searching with both the Cochrane Library and PubMed.

We would suggest the following steps:

1. Go to www.pubmed.gov and select Clinical Queries (left hand menu)

2. Select the appropriate Category (usually ‘therapy’ which is the default)

3. Type in the most crucial element of your PICO search (usually the I or the P)

4. If your search returns no articles then click the ‘Broad’ scope

5. If your search returns more than 30 articles then try adding more terms, e.g, if you used only the ‘I’ now try searching the I AND P (not use capitals for the AND)

6. Select the best single article (eg the largest or longest trial NOT necessarily the most recent). Please record why you chose the article you did.

The following pages have some further tips on where and how to go about searching.


http://www.pubmed.gov/

Searching Tips and Tactics

ORFinds studies containing either of the specified words or phrases. For example, child OR adolescent finds articles with either the word child or the word adolescent.

ANDFinds studies containing both specified words or phrases. For example, child AND adolescent finds articles with both the word child and the word adolescent.

NEAR Like AND it requires both words but the specified words must also be within about 5 words from each other.

NOTExcludes studies containing the specified word or phrase. For example, child NOT adolescent means studies with the word “child” but not the word “adolescent”. Use sparingly.

Limits Articles retrieved may be restricted in several ways, e.g, by date, by language, by whether there is an abstract, etc.

( )

Use parentheses to group words. For example, (Child OR adolescent) AND (hearing OR auditory) finds articles with one or both “child” and “adolescent” and one or both of the words “hearing” or "auditory"

*Truncation: the “*” acts as a wildcard indicating any further letters, e.g, child* is child plus any further letters and is equivalent to (child OR childs OR children OR childhood).

[ti] or :tiFinds studies with the word in the title. For example, hearing [ti] (in PubMed) and hearing:ti (in Cochrane) finds studies with the word hearing in the title.

[so] or :so Retrieves studies from a specific source, e.g., hearing AND BMJ [so] finds articles on hearing in the BMJ.

MeSHMeSH is the Medical Subject Headings, a controlled vocabulary of keywords which may be used in PubMed or Cochrane. It is often useful to use both MeSH heading and text words.


(furunc* OR (staphylococc* NEAR skin)) AND recur*:TI

truncation and wildcard (*) NEAR = AND plus words close together

Group words with ( )BOOLEANS IN CAPITALS Word must be in TITLE

(furunc* OR (staphylococc* NEAR skin)) AND recur*:TI

truncation and wildcard (*) NEAR = AND plus words close together

Group words with ( )BOOLEANS IN CAPITALS Word must be in TITLE

Session 3: Prepare a critically appraised topic

You should aim to set aside 2-3 hours to prepare you brief presentation at your final session. For this you will need:

1. To identify an article you found during the library session, and get the full text article

2. To critically appraise the article using the appropriate appraisal sheet (see extra readings for systematic review and diagnosis appraisal sheets).

3. Prepare a brief presentation – you will be given an single OHP (see attached example) but are welcome to use other methods. For other examples you might look at

(i) the CATbank on the CEBM website (www.cebm.net) or (ii) the BestBets: www.bestbets.org which has CATs for A&E

STRUCTURE OF YOUR PRESENTATION (with guide times)1. Describe the clinical situation and the clinical question (PICO) you need to answer. (2 mins)

2. Describe your search (1 min)

3. Write a brief description of the question (PICO) and methods of the study. Appraise the validity of the study. (3 mins)

4. State how the study applies to the patient you identified. (1 min)

A template for this is attached, but you are free to use another approach if you wish.

*Note: If you wish you may download CATMAKER from the CEBM website (www.cebm.net - the downloads section) to assist with writing your CAT. CATMaker structures the critical appraisal process, does the needed calculations for you, and allows you to print out the summary results.



http://www.bestbets.org/


Critically Appraised Topic PresentationExample

1. The patient & clinical questionA 43 year old male asked for some repeat prescriptions and advice about preventing deep vein thrombosis on a 12 hour flight (his brother had had one last year). You suggest stockings as the most effective prevention.

Question (PICO): In patients on long flights(P), do compression stockings (I) prevent DVT (O)?

2. search strategy

(a) PubMed: Clinical Queries (with therapy filters)(b) flight* AND stocking* AND DVT (c) 6 papers including 2 separate trials(d) The Scurr article was the larger trial, and quality appeared equal

3. The study – the question and appraisal

Study Question: In patients on flights over 8 hours in economy class, do Grade-I below-knee compression stockings, compared to no stocking, prevent ultrasound-detected DVT?

Randomisation: was by sealed envelope (not ideal) but lead to reasonable balance (See Table1) though more females appeared to receive stockings than males.Ascertainment: there was an 86% followup and ultrasound in each arm; this is adequate.Measurements: though stockings were removed pre-ultrasound, the sonographer may have seen the stocking mark and hence been unblinded.

The study has some flaws, but these are probably insufficient to explain the size of the results.

4. The resultsDVT occurred in 12% of the No Stocking group and 0% of the Stocking group.

Relative Risk Reduction of 100% and an absolute risk reduction of 12% (95%CI 69-100)

The NNT (number needed to treat) is 9. However, there was a small increase in superficial thrombophlebitis.

5. How the results apply.My patient is a little younger than the average of 62years seen in the trial, and hence probably at somewhat lower risk.


Nevertheless, this is a simple cheap and effective prevention procedure, which I would recommend to him.


Session Three: Presentations

The aim of this session is to produce and present a short a Critically Appraised Topic (CAT), and to discuss any issues and difficulties you have had with the group and your tutor.

For your brief presentation: Please hand a copy of your review and paper to the tutor before presenting. You will have about 7 minute to present and 3 minutes for discussion This should require about 2-3 overheads – e.g., one for the patient, one for the search and paper, and one for application to the individual patient.


Critically Appraised Topic PresentationTemplate

1. Give a description of the clinical situation and the clinical question you need to answer.

Question (PICO):

2. Give your search strategy including: (a) database used, (b) search terms used, and (c) number of papers identified, and (d) why did you choose the particular article?

3. What was the question of the study. Appraise the validity of the study

4. What were the results of the study?

5. State how the study applies to the patient you identified.








Glossary (From the EBM Journal BMJ Publishing)

TERMS USED IN THERAPEUTICSAllocation concealed: deemed to have taken adequate measures to conceal allocation to study group assignments from those responsible for assessing patients for entry in the trial (eg, central randomisation; sequentially numbered, opaque, sealed envelopes; sealed envelopes from a closed bag; numbered or coded bottles or containers; drugs prepared by the pharmacy; or other descriptions that contain elements convincing of concealment).

Allocation not concealed: deemed to have not taken adequate measures to conceal allocation to study group assignments from those responsible for assessing patients for entry in the trial (eg, no concealment procedure was undertaken, sealed envelopes that were not opaque, or other descriptions that contain elements not convincing of concealment).

Unclear allocation concealment: the authors of the article did not report or provide us with a description of an allocation concealment approach that allowed for classification as concealed or not concealed.

Blinded: any or all of the clinicians, patients, participants, outcome assessors, or statisticians were unaware of who received which study intervention. Those that are blinded are indicated in parentheses. If "initially" is indicated (eg, blinded [patients

and outcome assessor initially]), the code was broken during the trial, for instance, because of adverse effects.

Blinded (unclear): the authors did not report or provide us with an indication of who, if anyone, was unaware of who received which study intervention.

Unblinded: all participants in the trial (clinicians, patients, participants, outcome assessors, and statisticians) were aware of who received which study intervention.

When the experimental treatment reduces the risk for a bad eventRRR (relative risk reduction): the proportional reduction in rates of bad events between experimental (experimental event rate [EER]) and control (control event rate [CER]) patients in a trial, calculated as |EER-CER|/CER and accompanied by a 95% confidence interval (CI).

ARR (absolute risk reduction): the absolute arithmetic difference in event rates, |EER-CER| NNT (number needed to treat): the number of patients who need to be treated to prevent one additional bad outcome; calculated as 1/ARR, rounded up to the next highest whole number, and accompanied by its 95% CI.

When the experimental treatment increases the probability of a good eventRBI (relative benefit increase): the increase in the rates of good events, comparing experimental and control patients in a trial, also calculated as |EER-CER|/CER.

ABI (absolute benefit increase): the absolute arithmetic difference in event rates, |EER-CER|.

NNT: calculated as 1/ABI; denotes the number of patients who must receive the experimental treatment to create one additional improved outcome in comparison with the control treatment.

When the experimental treatment increases the probability of a bad eventRRI (relative risk increase): the increase in rates of bad events, comparing experimental patients to control patients in a trial, and calculated as for RBI. RRI is also used in assessing the effect of risk factors for disease.


ARI (absolute risk increase): the absolute difference in rates of bad events, when the experimental treatment harms more patients than the control treatment; calculated as for ABI.

NNH (number needed to harm): the number of patients who, if they received the experimental treatment, would lead to one additional person being harmed compared with patients who receive the control treatment; calculated as 1/ARI.

Confidence interval (CI): the CI quantifies the uncertainty in measurement; usually reported as 95% CI, which is the range of values within which we can be 95% sure that the true value for the whole population lies.

Weighted event rates: the contributions of individual studies to the total in a meta-analysis, determined by the sample size and the number of events in each study.

TERMS USED IN DIAGNOSISSensitivity: the proportion of patients with the target disorder who have a positive test result (a/[a + c]) (figure).

Specificity: the proportion of patients without the target disorder who have a negative test result (d/[b + d]) (figure).

Pretest probability (prevalence): the proportion of patients who have the target disorder, as determined before the test is carried out ([a + c]/[a + b + c + d]) (figure).

Pretest odds: the odds that the patient has the target disorder before the test is carried out (pretest probability/[1 — pretest probability]).

Likelihood ratio (LR): the ratio of the probability of a test result among patients with the target disorder to the probability of that same test result among patients who are free of the target disorder. The LR for a positive test is calculated as sensitivity/(1 — specificity). The LR for a negative test is calculated as (1 — sensitivity)/specificity.

Post-test odds: the odds that the patient has the target disorder after the test is carried out (pretest odds x LR).

Post-test probability: the proportion of patients with that particular test result who have the target disorder (post-test odds/[1 + post-test odds]).



3-day EBM workshop exercises€¦ · Web viewThe primary purpose of EBM sessions is to give you concrete experience in using searching and critical appraisal skills and in the context

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