EBM

Question 1

5 main steps of EBM

Answer 1

Define a clinical question, find evidence, appraise evidence, apply evidence to patient, communicate evidence to patient

Question 2

Validity questions for therapy (6)

Answer 2

• Was the assignment of pxs to treatment randomized?
• Was follow-up sufficiently long and complete?
• Were pxs analyzed in groups to which they were randomized?
• Were pxs and clinicians both blind?
• Were groups treated equally?
• Were groups similar at start of the trial?

Question 3

Intention to treat

Does it over / underestimate the effect of the experimental intervention?

Answer 3

• Intention to treat (ITT) - Pxs are analyzed according to the group to which they were randomized. Preserves the value of randomization, providing for an unbiased comparison of groups
• ITT often underestimates the effect of the experimental intervention.
• Not using ITT will often overestimate the effect of the experimental intervention.

Question 4

Importance questions for therapy (2)

Answer 4

• What was the magnitude of the treatment effect?

* How precise is the estimate of the treatment effect? How representative is the sample compared to the population?

Question 5

Relative risk reduction

Same formula as what?

Answer 5

• Relative risk reduction (RRR; aka Efficacy) = (CER – EER) / CER = 1 – RR
• Same formula for relative benefit increase (RBI)

Question 6

Formula for number needed to treat

Answer 6

Number needed to treat (NTT) = 1 / ARR

Question 7

What does a confidence interval tell you?

Answer 7

Tells the range w/in which the true effect of the intervention likely lies.

Question 8

For which values do you not want the confidence interval to include zero? (3)

Answer 8

RRR, ARR, ABI

Question 9

How is pre-test probability determined? (4)

Answer 9

Determine pre-test prob w/ clinical experience, epidemiology literature, consultation, or prevalence of disease

Question 10

Validity questions for diagnosis (4)

Answer 10

• Was there an independent blind comparison to a reference (gold) standard?
• Was the test evaluated in an appropriate spectrum of patients?
• Was the reference standard applied regardless of the test result?
• Was the test validated in a second, independent group of patients?

Question 11

Importance question for diagnosis

Answer 11

Can this test distinguish pas w/ and w/o the diagnosis?

Question 12

Does sensitivity / specificity rule in or rule out?

Answer 12

Sensitivity rules out

Specificity rules in

Question 13

Likelihood ratio definition
Positive formula
Negative formula

Answer 13

• Likelihood ratio (LR) = prob of a clinical features in px w/ disease / prob of same clinical feature in px w/o the disease
• Positive LR = sens / (1 – spec)
• Neg LR = (1 – sens) / spec

Question 14

Conclusive positive / negative LR

Not helpful positive / negative LR

Answer 14

Conclusive positive is >10
Conclusive negative is less than 0.1
Not helpful positive is 1-2
Not helpful negative is 0.5-1