Important Calculations

Question 1

ARP formula.

Answer 1

Attributable Risk Percent

ARP exposed = 100 × [(risk in exposed – risk in unexposed)/risk in exposed]

This basic definition can be used to derive an equivalent formula involving relative risk (RR):

ARP exposed = 100 × [(RR – 1)/RR], where RR = risk in exposed/risk in unexposed

Question 1

RR Calculations.

Answer 1

RR = IR of exposed/IR of those unexposed

RR = (risk of disease in Treatment A) / (risk of disease in Treatment B)

RR = treatment rate / control rate

Question 2

ARR what it stands for and calculation.

Answer 2

Absolute risk reduction (ARR)
ARR = control rate – treatment rate

Question 3

RRR what it stands for and calculation.

Answer 3

Relative risk reduction

RRR = ARR / control rate
RRR= 1-RR
RRR= (Riskcontrol - Risktreatment)/Riskcontrol

Question 4

NNT what it stands for and calculation.

Answer 4

NNT = 1 / ARR

Question 5

Meaning of NNT.

Answer 5

Number of individuals who need to be treated to prevent a negative outcome in 1 patient

Question 6

Meaning of RRR.

Answer 6

Percentage indicating relative reduction in the treatment event rate compared to the control group

Question 7

Meaning of ARR.

Answer 7

Percentage indicating the actual difference in event rate between control & treatment groups

Question 8

Meaning of ARP.

Answer 8

The attributable risk percent in the exposed (ARP exposed) is an important measure of the impact of a risk factor.

ARP exposed represents the excess risk in an exposed population that can be explained by exposure to a particular risk factor.