Evidence Based Medicine

Question 1

EBM - formula

AR, ARR, RR, RRR, NNT, OR

Answer 1

Absolute risk
- number of events in treated or control group, divided by number of people in that group

Absolute risk reduction
- ARC - ART

Relative risk
- ART/ARC

Relative risk reduction

• (ARC-ART)/ARC
• 1 - RR

Number needed to treat
- 1/ARR

Odds ratio

• odds that a case was exposed/odds that a control was exposed
• AD/BC

Question 2

Sensitivity

Answer 2

Sensitivity: how often a test shows pathology when it is present.

Question 3

Specificity

Answer 3

Specificity: how often a test is normal when no pathology is present.

Question 4

Negative predictive value

Answer 4

Negative predictive value: likelihood of the patient not having the disease when the test is negative.

Question 5

Positive predictive value

Answer 5

Positive predictive value: likelihood of the patient having the disease when the test is positive.

Question 6

Odds ratio

Answer 6

Odds ratio: association between an exposure and outcome.
● OR = 1 (no difference)
● OR >1 (negative)
● OR <1 (protective)

Question 7

Number needed to treat

Answer 7

Number needed to treat: number of people needed to be treated to achieve one good outcome or prevent one adverse outcome.

Question 8

False negative

Answer 8

False negative: diseased person incorrectly identified as healthy.

Question 9

False positive

Answer 9

False positive: health person incorrectly identified as diseased.

Question 10

Incidence

Answer 10

Incidence: number of new cases of disease occurring in a defined population within a specified period of time.

Question 11

Prevalence

Answer 11

Prevalence: total number of individuals who have the disease at a particular time in a population.

Question 12

Case control

Answer 12

Case control (retrospective): observational study in which two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute.

Question 13

Cross-sectional

Answer 13

Cross-sectional (or prevalence): observational study that analyzes data from a population, or a representative subset,
at a specific point in time

Question 14

Meta-analysis

Answer 14

Meta-analysis: systematic assessment of randomised controlled trials by merging data to draw a ‘firmer’ conclusion from larger numbers or subjects.

Question 15

Cohort study

Answer 15

Cohort (or prospective): longitudinal study that samples a cohort, performing a cross-section at intervals through time

Question 16

Clinical controlled trial

Answer 16

Clinical controlled trial: The comparison group receives a placebo, another treatment, or no treatment at all.