Evidence-Based MedicinePrognosis

Dr. Sompid KintarakDepartment of Stomatology

Faculty of Dentistry, Prince of Songkla University

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.

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 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.

Hierarchy of evidence

Anecdotal case report

Cross-sectional survey

Case series without a control

Case-control observational study

Cohort study with a literature control

Analyses using computer databases

Cohort study with a historical control group

Unconfirmed randomized controlled clinical trial

Confirmed definitive randomized controlled clinical trials

Systematic review of randomized controlled clinical trials

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.

Are The Results Valid?

Was this a well designed study in a relevant population?

The best design of study to answer a prognosis question is a prospective cohort study.

Are The Results Valid?1. Was a defined, representative sample of patients assembled

at a common (usually early) point in the course of their disease? กลุ่��มตั�วอย่�างที่��ศึ�กษา อย่��ในระย่ะเดี�ย่วก�นของโรคหร�อไม� โดีย่ที่��วไปม�กจะเป#นระย่ะเร$�มตั%นของโรค

2. Was patient follow-up sufficiently long and complete?

ผู้�%ป'วย่ไดี%ร�บการตั$ดีตัามผู้ลุ่ครบถ้%วนแลุ่ะนานพอหร�อไม�3. Were objective outcome criteria applied in a “blinded”

fashion?

ม�การ “blind” ลุ่�กษณะพ�-นฐานข%อม�ลุ่ผู้�%ป'วย่แลุ่ะป/จจ�ย่ตั�าง ๆ ที่��จะม�ผู้ลุ่ตั�อการพย่ากรณ1โรคแก�ผู้�%ประเม$นผู้ลุ่ลุ่�พธ์1ที่��ศึ�กษาดี%วย่ เพ��อไม�ให%เก$ดีการลุ่3าเอ�ย่ง

4. If subgroups with different prognosis are identified:

- Was there adjustment for important prognostic factors?

- Was there validation in 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)?

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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”).

Clinically Important?

How likely are the outcomes over time?1. Percentage “survival” at a particular point

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

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

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?

References. บที่ที่�� 3. การประเม$นค�ณภาพของข%อม�ลุ่ ใน: การเร�ย่นการสอนการ

แพที่ย่1เชิ$งประจ�กษ1 – Learning and teaching of evidence-based medicine. พ$มพ1คร�-งที่�� 1. กลุ่��ม Promoting evidence-based medicine into clinical practice คณะแพที่ย่ศึาสตัร1 มหาว$ที่ย่าลุ่�ย่สงขลุ่านคร$นที่ร1 . 2548.หน%า -2772.

• Sackett DL, Straus SE, Richardson WS, Rosenberg W, Haynes RB. Evidence-based medicine – how to practice and teach EBM. Second ed. Edinburgh: Churchill Livingstone, 2000. pp 95-103.

• Clarkson J, Harrison JE, Ismail AI, Needleman I, Worhtington H. Evidence based dentistry for effective practice. London: Martin Dunitz, 2003.