Evidence Based Practice

Question 1

What is relative risk ratio (RRR)?

Answer 1

The probability of an event happening in the intervention group compared to the control group - e.g 5 in 100 people might be sick in the intervention group and 15 in a 100 may be sick in the control group. The relative risk ratio would be (5/100)/(15/100) = 0.33

Question 2

What is the absolute risk reduction (ARR)?

Answer 2

The difference in probability of an event occurring in the intervention and control group e.g. absolute risk reduction would be 15% (derived from 15/100) minus 5% (derived from 5/100) and so ARR would be 10%.

ARR is always written as a percentage

Question 3

What is number needed to treat (NNT)?

Answer 3

NNT is the inverse of ART i.e. (1/ART) so in this case it would be 1/0.1 (ARR is displayed as number here not a percentage) so NNT would be 10 - this treatment is successful for 1 in ten pxs. (or that treatment needs to be given to ten pxs in order for one to benefit from it).