Evidence-Based MedicineWeek 3 - Prognosis

Department of Medicine - Residency Training ProgramTuesdays, 9:00 a.m. - 11:30 a.m., UW Health Sciences Library

Steps in Practicing EBM1. Convert the need for information into

an answerable question.2. Track down the best evidence with

which to answer that question.3. Critically appraise the evidence for its

validity, impact, and applicability.4. Integrate the evidence with our clinical

expertise and our patient’s characteristics and values.

Review Last Week’s Session

Weeks 3 & 4 - Prognosis“Fourth, despite its importance in clinical decision making,

prognosis gets short shrift relative to research in diagnosis or treatment. In 2005 to 2006, the editors hope to publish more papers that give clinicians and their patients useful information about prognosis. We are most interested in articles that highlight important clinical outcomes and how frequently such outcomes occur; that provide precise estimates of how well prognostic indicators predict important outcomes; and that communicate this information so that clinicians can easily understand and use it. We also welcome systematic reviews that clearly describe limitations of current knowledge about prognosis, that summarize information that would be useful for patients with particular prognostic findings, and that provide clinicians with a meaningful template for sharing prognostic information with their patients.”

Excerpted from: The Editors. Annals 2004 -2005. A peak back and a look forward. Ann Intern Med. 2005;142:1016-1018.

Steps in Practicing EBM1. Convert the need for information into

an answerable question.2. Track down the best evidence with

which to answer that question.3. Critically appraise the evidence for its

validity, impact, and applicability.4. Integrate the evidence with our clinical

expertise and our patient’s characteristics and values.

The Answerable Question

Good questions are the backbone of practicing

EBM. It takes practice to ask the well-formulated

question.

Well-Built Clinical ?’s• Directly relevant to the care of the

patient and our knowledge deficit.• Contains the following elements:

– the patient or problem being addressed

– the intervention or exposure being considered

– the comparison intervention or exposure, when relevant

– the clinical outcomes of interest.

Well Formulated ?’s• Focus scarce learning time on evidence

directly relevant to patient’s needs and our particular knowledge needs.

• Suggest high-yield search strategies.• Suggest forms that useful answers might take.• Help us to model life-long learning techniques

for our colleagues and students.• Are answerable and, thus, reinforce the

satisfaction of finding evidence that makes us better, faster clinicians.

Prognosis Questions

Steps in Practicing EBM1. Convert the need for information into

an answerable question.2. Track down the best evidence with

which to answer that question.3. Critically appraise the evidence for its

validity, impact, and applicability.4. Integrate the evidence with our clinical

expertise and our patient’s characteristics and values.

ResourcesMETA-SEARCH ENGINESPrimeAnswers TRIP+ SUMSearch

SYSTEMATIC REVIEWS/META-ANALYSESCochrane Library PubMed Clinical Queries using Research Methodology Filters

EVIDENCE GUIDELINES/SUMMARIESAHRQ Evidence Reports Clinical Evidence AHRQ Preventive Services

CLINICAL RESEARCH CRITIQUESACP Journal Club 1996- Bandolier 1994- BestBETs

CASE REPORTS/SERIES, PRACTICE GUIDELINES, ETCNational Guideline ClearinghousePubMed

Steps in Practicing EBM1. Convert the need for information into

an answerable question.2. Track down the best evidence with

which to answer that question.3. Critically appraise the evidence for its

validity, impact, and applicability.4. Integrate the evidence with our clinical

expertise and our patient’s characteristics and values.

Strategies for Critical Appraisal of Studies on Prognosis

Clinical ImportanceValidity

Applicability

Strategies for Critical Appraisal of Studies on Prognosis

Validity

Are The Results Valid?1. Assembled a defined, representative

sample of patients at a common point in course of disease.

2. Follow-up of patients sufficiently long and complete.

3. Objective outcome criteria applied in a “blinded” fashion.

4. If subgroups with different prognosis:- Adjustment for other important prognostic factors.

- Validation of an independent group of “test-set” patients.

Types of Studies• Most studies will be “cohort studies”.• RCT’s (particularly placebo arms) can

generate information about prognosis of disease.

• Case-control studies can be useful but fail to provide estimates of absolute risk. Mostly encountered when the outcome is rare or required duration of follow-up is long.

The Cohort of Patients• How close to “ideal” does the study

come in terms of how the disease was defined and how the participants were assembled (“full spectrum of illness”).– e.g. avoid “referral bias” if possible

• Is this an “inception” cohort or is there uniform entry point (for late stage disease)?

start smoking atherosclerosis lung cancer death

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Follow-up• To know if length of follow-up sufficient

often requires general knowledge about disease.

• Complete follow-up is critical. Failure is influenced both by better than average and worse than average clinical course.– “5% and 20%” rule.– worst-case scenario/sensitivity analysis

Outcome Criteria

• Extreme outcomes are easy to recognize. Outcomes in between require judgement and thus require standard criteria.

• Those making judgement are kept “blind” to patients’ clinical characteristics and prognostic factors.

Adjustment and Validation• If subgroups with different prognosis

then was there statistical adjustment for other important prognostic factors (statistical adjustment is not explanatory).

• To the extent that adjustment is not explanatory, the first time a prognostic factor is identified, is there a confirmatory data set of patients (“derivation set” and “validation sets”).

Strategies for Critical Appraisal of Studies on

Prognosis

Clinical Importance

Clinically Important?1. How likely are the outcomes over

time?1. Percentage “survival” at a particular point in

time.2. Median survival.3. Survival curves.

2. How precise are the prognostic estimates?95% CI - range of values within which we can be

95% sure that the population value lies

Survival Curves

1 year survival 95%Median survival unknown

1 year survival 20%Median survival 3 months

1 year survival 20%Median survival 9 months

1 year survival 20%Median survival 7 months

Strategies for Critical Appraisal of Studies on Prognosis

Applicability

Applicable to Our Patient?

1. Are the study patients similar to our own?

2. Will the evidence make a clinically important impact on our conclusions about what to offer or tell our patient?

Questions?

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