Evaluating treatments

• Safe

• Effective

• How does it compare to existing alternatives?

• Cost

• Acceptable

Assessing safety

Assessing efficacy

• RRR

• ARR

• NNT

120 patients randomised to colchicine. 120 randomised to placebo

45 in the placebo group develop recurrent or incessant pericarditis; Compared to 20 in the colchicine group (p<0.001)

CALCULATE: Odds Ratio; Relative Risk; Relative Risk Reduction; Absolute Risk Reduction; NNT;Percentage chance that a patient you treat with colchicine will benefit

Examples

Colchicine for acute pericarditisBad outcome (incessant or recurrent pericarditis)

Good outcome

Colchicine 20 100

Placebo 45 75

Odds of bad outcome with colchicine = 20 / 100 = 0.2Odds of bad outcome with placebo = 45 / 75 = 0.6

OR = 0.2 / 0.6= 0.33

ODDS RATIO

Colchicine for acute pericarditisBad outcome (incessant or recurrent pericarditis)

Good outcome

Colchicine 20 100

Placebo 45 75

RR = Risk in intervention group / Risk in control group

RR = (20/120) / (45/120)= 0.44

RELATIVE RISK

Colchicine for acute pericarditisBad outcome (incessant or recurrent pericarditis)

Good outcome

Colchicine 20 100

Placebo 45 75

RRR = % reduction in relative risk with the intervention

RRR = [ (45/120) - (20/120) ] / (45/120)= 0.56

Colchicine for acute pericarditisBad outcome (incessant or recurrent pericarditis)

Good outcome

Colchicine 20 100

Placebo 45 75

ARR = % reduction in absolute risk with the intervention

ARR = (45/120) - (20/120) = 20.8%

Colchicine for acute pericarditisBad outcome (incessant or recurrent pericarditis)

Good outcome

Colchicine 20 100

Placebo 45 75

NNT = 1 / ARR

NTT = 1 / 0.28 = 4.8