WELCOME TO THE EVIDENCE BASED MEDICINE TASK TEAM

Leader:              Howaida Hashim Ph.D. ELD (ABB)

 Coordinator:      Haifa Wahbi MD. MRCOG

 AIM:

Our aim is to improve patient care by developing and promoting evidence-based health care, and to provide support and resources to anyone who wants to practice or teach EBM. We have several resources to help with learning and using EBM. Contact us.

	WHAT IS EBM
	THE STEPS IN THE EBM PROCESS
	WHY IS EBM IMPORTANT?
	THE EBM PROCESS
	GLOSSARY OF TERMS
	REFERENCES
	THE LITERATURE SEARCH
	EVALUATING THE EVIDENCE
	USEFUL LINKS
	I would like to join EBM group, what to do?

What is EBM:

The most common definition of Evidence Based- Medicine (EBM) is taken from Dr. David Sackett. EBM is "the conscientious, explicit and judicious use of current best evidence in making decisions about the care of the individual patient. It means integrating individual clinical expertise with the best available external clinical evidence from systematic research." (Sackett D, 1996)

EBM is the integration of clinical expertise, patient values, and the best evidence into the decision making process for patient care. Clinical expertise refers to the clinician's cumulated experience, education and clinical skills. The patient brings to the encounter his or her own personal and unique concerns, expectations, and values. The best evidence is usually found in clinically relevant research that has been conducted using sound methodology. (Sackett D, 2002)

The evidence, by itself, does not make a decision for you, but it can help support the patient care process. The full integration of these three components into clinical decisions enhances the opportunity for optimal clinical outcomes and quality of life. The practice of EBM is usually triggered by patient encounters, which generate questions about the effects of therapy, the utility of diagnostic tests, the prognosis of diseases, or the etiology of disorders.

Evidence-based medicine requires new skills of the clinician, including efficient literature searching, and the application of formal rules of evidence in evaluating the clinical literature. 

The practice of EBM is achieved by:

(1)   Converting the need for information into answerable questions;

(2)   Tracking down the best evidence with which to answer these questions;

(3)   Critically appraising the evidence for validity, importance, and applicability;

(4)   Integrating this appraisal with our clinical expertise and our patient’s unique biology, values and circumstances; and

(5)   Evaluating our effectiveness and efficiency in executing steps 1 to 4 and finding ways to improve them for the future.

Recent developments that have made the practice of EBM more attainable include international groups reviewing the literature, development of evidence-based journals, availability of improved search strategies and electronic search services.

One of the biggest problems with EBM is simply the difficulty in quantifying clinical outcomes. All areas of clinical practice, including reproductive medicine, suffer from the lack of good outcomes data. Clinical research is often deficient and most physicians have a limited understanding of interpreting the literature and optimizing the use of the data. For example, it is necessary to know the different types of study designs and their limitations. The US Preventive Services Task Force rating scale for experimental design is either a randomized controlled trial (I) or a nonrandomized controlled trial (II-1). Observational studies are cohort or case-control studies (II-2), multiple time series before and after intervention (II-3) or descriptive studies, consensus panel, or expert opinion (III).

Evidence-based medicine has its limitations. First, no studies have conclusively proven in a prospectively randomized trial that EBM has an effect on outcomes, because no one has overcome the problems of study design, size and follow-up that would be necessary. The principles of evidence-based medicine can be misapplied and the literature misinterpreted. Quantifying outcomes can be difficult, instruments can read incorrectly, measurements by the investigator are potentially biased, statistical significance can be confused with clinical relevance, data can be limited or not available when it is needed, multiple step algorithms are complex and publication bias can limit the reporting of negative outcomes.

But studies have shown that those patients who have evidence-based therapy have better outcomes than those who do not. Clinical protocols for standardizing care have also been shown to be an effective tool to improve quality and efficiency of care. Better methods to provide more informed consent to patients given the many variables and personal perspectives are needed, and more sophisticated interactive information systems are needed.

The Steps in the EBM Process:

Why is EBM important?

Information Needs

Studies of information-seeking habits of physicians, have shown that when asked, physicians reported that their practice generated about 2 questions for every 3 patients. Only 30% of physicians' information needs were met during the patient visit, usually by a colleague. Reasons for not using printed resources included office textbook collections too old, lack of knowledge of appropriate resources, and lack of time to find the needed information. (Covell DG, 1995)

When actually observed, investigators found that physicians had about 5 questions for each patient. 52% of these question could be answered by the medical record or hospital information system. 25% could have been answered by published information resources such as textbooks or MEDLINE. (Osheroff JA, 1991)

However, studies have also shown that when clinicians have access to information, it changes their patient care management decisions.

In 1998, Dr. David Sackett, using an "evidence cart" on rounds, reported that of 71 information searches to answer clinical questions, 37 (52%) confirmed the management decision, but 18 (25%) lead to a new therapy or diagnostic test and 16 (23%) corrected a previous plan. (Sackett D, 1998)

Similar results were report by Crowley et al in 2003. The CAR study showed that of 520 clinical questions for which answers were sought in the medical literature, in 53% of these cases the literature confirmed the management decision, but in 47% of these cases the literature changed the medication, diagnostic test, or prognostic information given to the patient. (Crowley S, 2003)

The EBM Process

Glossary of Terms

Absolute risk and its reduction

This is the percentage of subjects in any group or sub-group that experiences a discrete bad outcome such as death or admission to the hospital. An efficacious therapy serves to reduce that risk. For example, if 15% of the placebo group died and 10% of the treatment group died, the absolute reduction in the risk of death is 5%.

Accuracy

The proportion of all test results (positives and negatives) which agreed with the gold standard.

Applicability (also called external validity, generalizability, relevance)

This is the degree to which the results of an observation, study, or review are likely to hold true in your practice setting.

Bayes' Theorem

This is a simple formula that says that if a particular test result is twice as likely to occur in patients with a disease, condition, or injury than in patients without, then, it is twice as likely that the patient with the result being tested for actually has the disease as compared to any randomly selected similar patient who has not been tested. If you don't like thinking about things like this, just use the nomogram in the users guides or the calculator on the diagnosis appraisal page.

Bias

This is any factor which might change the results of a study from what they would have been if that factor were NOT present. The direction of bias may be unpredictable. For example, giving a team a ten point advantage might seem to give that side an advantage but some teams actually play much better when they have to come from behind! The validity of a study is integrally related to the likelihood that the results have been biased by factors extraneous to the study design.

Blinding

The "masking" or concealment from study subjects, caregivers, or others involved in the study of any detail(s) of the study which could introduce Bias. For example, not telling patients or doctors which patient gets placebo or actual drug; or not telling radiologists the clinical assessment of patients whose films they are reading.

Case-control study

This might be considered a randomized controlled trial played backwards. People who get sick or have a bad outcome are identified and "matched" with people who did better. Then, the effects of the therapy or harmful exposure which might have been administered at the start of the trial are evaluated. In other words, you first find the people who did poorly and then look at the therapy or exposure and compare it to people who didn't get the therapy. Needless to say, this is a crude way of doing a study. When the effect of interest is HARM, this may actually be the only ethical way of doing the study.

Case report

This includes single case reports and published case series'. These are searchable as a separate category in the MEDLINE database

C.A.T.

see critically appraised topic

Clinical significance

Results are clinically significant when they make enough difference to you and your patient to justify changing your way of doing things. For example, a drug which is found in a megatrial of 50,000 adults with acute asthma to increase FEV1 by only 0.5% (P value<.0001) has failed this test of significance.

Cochrane Collaboration

An international organized effort to organize all existing clinical studies into systematic reviews easily accessible to practicing clinicians and to otherwise facilitate the process of bringing clinical evidence to bear on decision making in patient care.

Cohort study

Also called a "prospective observational study", this design follows a group of patients, called a "cohort", over time to determine general outcome as well as the outcomes of different subgroups.

Co intervention

A therapy or other ancillary treatment which is NOT under investigation which is given to study patients.

Confidence intervals

An interval around an observed parameter such as relative risk which is guaranteed to include the true value to some level of confidence (usually 95%). That level of confidence is only justified to the extent that bias is absent from the study. A well known election poll advertises itself "this poll is accurate to within 2 percentage points 99% of the time." This is a way of saying, in language aimed at voters (perhaps a skewed sample from the standpoint of IQ) that the 99% CI around the reported percentages is + 2.

Controlled clinical trial

Any study which compares two groups by virtue of different therapies or exposures fulfills this definition.

Critical appraisal

The process of assessing and interpreting evidence systematically considering its validity, results, and relevance. 

Critically appraised topic (C.A.T.)

A 1 or 2 page summary of a search and critical appraisal of the literature related to a focused clinical question. This summary should be kept in an easily accessible place so that it can be used to help make clinical decisions.

Dichotomous outcome

Any outcome measure in which there are only two possibilities, like dead/alive, admitted/discharged, graduated/sent to glue factory. Beware of potentially fake dichotomous outcome reports such as "improved/ not improved", particularly when derived from continuous outcome measures.

Double blind

A single blind study means that someone (patient or physician) does not know what is going on. Double blind means that at least two people (patient and physician) don't know what's going on. Triple blind might mean that the paper is written before the results are tabulated. The whole point is to prevent bias.

Effect size

The difference in measured outcomes attributed to a therapeutic intervention. This term is encountered in meta-analyses when different studies have measured different things.

Effectiveness

I buy a BMW which test drives miraculously on the dealer’s special runway. I then find that the roads in the area where I live have all been closed. This is a breakdown of effectiveness. See efficacy.

Efficacy

The BMW I have selected for a test drive blows all four tires, stalls out and crashes on the dealer’s special runway. I spend two days in the hospital. This is a breakdown in efficacy. See effectiveness.

Event rate

This is a term for absolute risk.

Exposure

Anything you can be exposed to: a drug, a surgical procedure, time, sexual harassment, rounds, even a diagnostic test. Most commonly encountered in therapy, prognosis or harm studies where the EFFECT of an "exposure" is the subject of the study.

External validity

See applicability.

Generalizability

See applicability.

Gold standard

No longer relevant in the realm of high finance from whence it originated, this term gained new life when it was decided that it should refer to a reference standard for evaluation of a diagnostic test. For the purposes of a study, the "gold standard" test is assumed to have 100% sensitivity and specificity. This may well constitute an exaggerated estimate of the reference test. Choice of the "gold standard" must therefore be evaluated in appraising a diagnosis study.

Harm-Benefit Line

On a graph of outcomes, this line divides results favoring therapy from results favoring the control.

Heterogeneity

Also called "homogeneity" but having nothing to do with sexual preference, this term is used to designate a statistical test used to determine whether results from a set of independently performed studies on a particular question are similar enough to make statistical pooling valid. Are the apples sufficiently red and the oranges sufficiently green to be able to add them up and report the total number of "orpples"? As in other matters, statistical tests do not guarantee clinical relevance.

Homogeneity

See heterogeneity.

Incidence

The rate at which an event occurs in a defined population over time. To be distinguished from prevalence.

Intention-to-treat

Intentions... that with which the path to hell is lined. Patients assigned to a particular treatment group by the study protocol should be retained in that group for the purpose of analysis of the study results no matter what happens. Patients redefined or dropped from a study early on as a result of protocol violations unlikely to create bias may validly be considered exceptions to this rule.

Internal validity

See validity.

Likelihood Ratio

An operator defined as the percentage of patients positive by gold standard for a particular disease, condition or injury who have a particular test result divided by the percentage of patients without the problem who have that same test result. A likelihood ratio of two means that the test result in question is twice as likely to come a patient with the problem as it is from a patient without the problem. The LR may be derived from reported sensitivity and specificity or from a clear understanding of the above definition. To see how the LR is used, see Bayes‘ Theorem; to actually use it, see the nomogram. To see how the Likelihood Ratio is generated, use the calculator

Meta-analysis

A review of a focused clinical question following rigorous methodological criteria and employing statistical techniques to combine data from independently performed studies on that question. To learn more, see the User’s Guide.

Nomogram for Likelihood Ratio

Null hypothesis

What do you do when you want others to be maximally impressed with what you do? You DECREASE EXPECTATIONS, then what you do accomplish looks even better! The null hypothesis is the assumption that there is no difference between the groups and that the treatment you are studying has no effect. Any difference in outcome actually observed between the groups is then evaluated in relationship to the "zero expectation" hypothesis.

Number needed to treat (NNT)

The number of patients who must receive a particular therapy for one to benefit. You might tell a patient that an NNT of 10 means that the chance that he/she will benefit in this way from the treatment is 1 in 10. To calculate NNT use the calculator.

Observational study

Any study of therapy, prevention or harm in which the exposure is not assigned to the individual subject by the investigator(s). A synonym is "non-experimental"; examples are case-control and cohort studies.

Odds ratio

The odds of an event, understood best by those who enjoy wagers, is the number of times it occurred (a) divided by the number of times it didn’t (b), or a/b. This contrasts with the probability of an event which is the number of times it occurred divided by the number of times it could have occurred, or a/a+b. The odds ratio is the ratio of the odds of an event in one group divided by the odds in another group. When the event rate or absolute risk in the control group is small (less than 20% or so), then the odds ratio is very close to the relative risk.

Placebo

The thing you give a study subject who has been assigned to the control group to make them think they are getting the treatment you are studying.

Point estimate

The exact result that has been observed in a study. The confidence interval tells you the range within which the result is likely to lie.

Post-test probability

The likelihood that your patient has the disease, condition or injury you are testing for at the moment the result of the test you (or someone) ordered is delivered to you. To calculate it you need the pretest probability or prevalence and also the likelihood ratio for the test in question. To do this, you could use Bayes theorem or, if you are lazy (and practical), use the nomogram.

Pre-test probability

At the point you order a diagnostic test, you already have some idea of how likely your patient is to have the disease, condition or injury in question. You think of this as small, medium or large. "Pretest probability" means putting a number on the estimate you have already made. A difference of 10% in either direction will not change the effect of the diagnostic test. Putting the number on your clinical estimate will, however, allow you to determine what the test result means, should you want to know. This is also called prevalence.

Prevalence

The proportion of people in a defined group who have a disease, condition or injury. In the context of diagnosis, this is also called "pre-test probability." To be distinguished from incidence.

Prospective study

Any study done forwards in time. This is particularly important in studies on therapy, prognosis or harm, where retrospective studies make hidden biases very likely.

Publication bias

A possible bias which can effect systematic overviews to the extent that studies on the question at hand with conflicting results may not have been published.

P value

The probability that the difference(s) observed between two or more groups in a study would occurred if there were no differences between the groups other than those created by random selection. The assumption underlying the p-value is the null hypothesis.

Power

The chance that an experimental study will correctly observe a statistically significant difference between the study groups. This may be considered the "sensitivity" of the study trial itself for detecting a difference when it is there.

Randomization

A technique which gives every patient an equal chance of winding up in any particular arm of a controlled clinical trial.

Randomized Controlled Trial

A controlled clinical trial in which the study groups are created through randomization.

Relative risk and its reduction

The probability of an event in one group divided by the probability of the same event in another group. Generally the event is a bad one and the rate in the therapy group (when it is a therapy study) is in the numerator. When a benefit has been observed, this ratio is less than one. Subtracting the ratio from one gives the relative risk reduction, which is the percentage by which the risk in the control group has been reduced by the therapy.

Reliability

Sometimes used loosely, this actually refers to the reproducibility of a measurement procedure. It is NOT the same as validity or applicability of a study.

Retrospective study

Any study in which the outcomes have already occurred before the study has begun.

Risk factor

Any aspect of an individual’s life, behavior or inheritance which increases the likelihood of a disease, condition or injury.

Sensitivity

The probability that a patient with a disease, condition or injury will test positive by a particular test for the problem.

Sensitivity analysis

An analytical procedure to determine how the results of a study would change if the facts were different or different studies included. This is chiefly important in meta-analysis or complex techniques such as decision analysis and cost-effectiveness analysis.

Specificity

The probability that patients without a particular disease, condition or injury will test negative for the problem by a particular test.

Statistical power

see Power

Statistical significance

A measure of how confidently an observed difference between two or more groups can be attributed to the study interventions. The p value is the most commonly encountered way of reporting statistical significance. The methods assume that the study is free of bias. Clinical significance is entirely independent from statistical significance.

Stratified randomization

A way of ensuring that the different groups in an experimental trial are balanced with respect to important factors which could effect outcome.

Spectrum

In a diagnosis study, the range of clinical presentations and of relevant disease advancement exhibited by the subjects included in the study.

Systematic overview

A formal review of a focused clinical question based on a comprehensive search strategy and structured critical appraisal.

Threshold Probabilities

The level of suspicion at which your clinical decision changes 

Utility

Particularly for a diagnostic test, this is a measure of whether the patient is truly better off as a result of the test. A test could have high sensitivity, specificity and good likelihood ratios and still have low utility if it is very invasive or poses other risks or inconvenience to the patient. It belongs under the section of a diagnostic review.

Validity

The degree to which the results of a study are likely to be true, believable and free of bias. This is entirely independent of the precision of the results (p value) and does not predict the of the results to your patients.

REFERENCES:

Bordley DR. Evidence-based medicine: a powerful educational tool for clerkship education. American Journal of Medicine. 102(5):427-32, 1997 May.

Covell, DG. Uman, CG. Manning, PR. Information needs in office practice: are they being met? Annals of Internal Medicine 103(4):596-599, Oct 1995.

Crowley SD, Owens TA, Schardt CM, Wardell SI, Peterson J, Garrison S, Keitz SA. A Web-based compendium of clinical questions and medical evidence to educate internal medicine residents. Acad Med 78(3):270-4, 2003 Mar.

Michaud G. McGowan JL. van der Jagt R. Wells G. Tugwell P. Are therapeutic decisions supported by evidence from health care research? Archives of Internal Medicine158(15):1665-8, 1998 Aug 10-24.

Osheroff JA. Forsythe DE. Buchanan BG. Bankowitz RA. Blumenfeld BH. Miller RA. Physicians' information needs: analysis of questions posed during clinical teaching. Annals of Internal Medicine 114(7):576-81, 1991 Apr 1.

Sackett, D. Evidence-based Medicine: How to Practice and Teach EBM. 2nd edition. Churchill Livingtone, 2000.

Sackett, D. Evidence-based Medicine - What it is and what it isn't. http://www.cebm.net/ebm_is_isnt.asp 1996.

Sackett DL, Straus SE. Finding and applying evidence during clinical rounds: the "evidence cart". JAMA 280(15):1336-8, 1998 Oct 21.

Tonelli, M.R. The philosophical Limits of Evidence-based Medicine. Academic Medicine 73(12):1234-1240, Dec 1998.

Well-Built Clinical Question

Richardson WS, Wilson MC, Nishikawa J, Hayward RSA. The well-built clinical question: a key to evidence-based decisions. ACP Journal Club. Nov-Dec 1995;123;A12.

The Literature Search 

Duke University, Medical Center, Ovid tutorial. http://www.mclibrary.duke.edu/training/ovid

PDQ Evidence-Based Principles and Practice, 1999, by Ann McKibbon, as a reference in search strategies for doing a literature search using MEDLINE, CINAHL Database of Nursing and Allied Health Literature, PsycINFO, and EMBASE/Excerpta MEDICA. Order information from B.C. Decker, Inc. at http://www.bcdecker.com

UNC-Chapel Hill, HSL, Database Searching learning module: http://www.hsl.unc.edu/services/tutorials/srchdbs/splash.htm

Evaluating the Evidence

Users' Guides to the Medical Literature from JAMA: Note: The full text of the Users' Guide series is available from the Centre for Health Evidence.

Guyatt GH ; Rennie D. Users' guides to the medical literature [editorial]. JAMA 1993 Nov 3; 270(17):2096-7.

Oxman AD ; Sackett DL ; Guyatt GH. Users' guides to the medical literature. I. How to get started. The Evidence-Based Medicine Working Group. JAMA 1993 Nov 3; 270(17):2093-5.

Therapy

Guyatt GH ; Sackett DL ; Cook DJ. Users' guides to the medical literature. II. How to use an article about therapy or prevention. A. Are the results of the study valid? Evidence-Based Medicine Working Group. JAMA 1993 Dec 1;270(21):2598-601.

Guytt GH ; Sackett DL ; Cook DJ. Users' guides to the medical literature. II. How to use an article about therapy or prevention. B. What were the results and will they help me in caring for my patients? Evidence-Based Medicine Working Group. JAMA 1994 Jan 5; 271(1):59-63.

Diagnosis

Jaeschke R ; Guyatt G ; Sackett DL. Users' guides to the medical literature. III. How to use an article about a diagnostic test. A. Are the results of the study valid? Evidence-Based Medicine Working Group. JAMA 1994 Feb 2;271(5):389-91.

Jaeschke R ; Guyatt GH ; Sackett DL. Users' guides to the medical literature. III. How to use an article about a diagnostic test. B. What are the results and will they help me in caring for my patients? The Evidence-Based Medicine Working Group. JAMA 1994 Mar 2; 271(9):703-7.

Etiology/Harm

Levine M ; Walter S ; Lee H ; Haines T ; Holbrook A ; Moyer V. Users' guides to the medical literature. IV. How to use an article about harm. Evidence-Based Medicine Working Group. JAMA 1994 May 25; 271(20):1615-9.

Prognosis

Laupacis A ; Wells G ; Richardson WS ; Tugwell P. Users' guides to the medical literature. V. How to use an article about prognosis. Evidence-Based Medicine Working Group. JAMA 1994 Jul 20; 272(3):234-7.

Useful links:

Oxford Centre for Evidence Based Medicine

http://www.ebm-first.com

http://www.hsl.unc.edu/services/tutorials/srchdbs/splash.htm

http://www.bcdecker.com

http://www.mclibrary.duke.edu/training/ovid

http://www.cebm.net/ebm_is_isnt.asp

Duke University Medical Center Library

Health Sciences Library, UNC-Chapel Hill

I would like to join EBM group, what to do?

Only members of the MEFS will be able to access the EBM task team facility. You will be redirected to the application of the MEFS membership form