Evidence Based MedicineIntroduction to Critical Appraisal

Jeffrey P Schaefer MSc MD FRCP FACP

October 21, 2010

Objectives

• You will:– define evidence based medicine– know where critical appraisal fits into EBM– list 5 important clinical questions– describe best research designs– know the basic approach to critical appraisal– be exposed to CA for each clinical question

What is Evidence Based Medicine?

What is Evidence Based Medicine

• Application of the best evidence to health problems within the context of the expertise and values of the patient, physician, and society.

• JP Schaefer

EBM Process

• Formulate a focused clinical question.

• Search for evidence.

• Critically appraise the evidence.

• Apply the evidence to your practice.

• Learnings are stored for future reference.

• Outcomes are reviewed.

The Essence of Critical Appraisal

• Three Questions– Are the results valid?– What are the results?– Do the results apply to my patient?

What Critical Appraisal is Not...

• It’s not about trashing an article– something can be learned from every article,

even if it’s how to design a better trial!

• It’s not about black and white answers– most studies have strengths and weaknesses– some studies are highly edited

• It’s not the only reason to embark on a course of action– other factors (harm, cost, patient values)

Five Clinical Questions• Harm

• Diagnosis

• Therapy

• Prognosis

• Prevention

• Also…– systematic reviews (e.g. meta-analyses)– econominc analyses– others

+ malignancy Gold Std + Gold Std -

Histology + 41 11 52

Histology - 7 346 353

48 357 405

SENS 41 / 48 = 0.854 = 85%

SPEC 346 / 357 = 0.969 = 97%

PPV 41 / 52 = 0.788 = 79%

NPN 346 / 353 = 0.980 = 98%

http://faculty.vassar.edu/lowry/clin1.html

Not sure: issue here is the false negatives.

General Issues• multiple strange questions in same article

• why differentiate lipoma from IM lipoma?

• how did 600 cases get to 405 cases?

• why exclude ‘rare forms’?

• how did molecular studies get to be gold-std?

• initial surgical tx was / is independent of pathology

• failure to provide CI for test characteristics

• accuracy is not very useful