Evidence-Based Practice for Nurses

that emerge from qualitative research are valued because they incorporate
the “patients’ voice into evidence based process” (p. 142). As such, qualitative
research deserves a place in the hierarchy of evidence although it may not be
considered equivalent to quantitative research findings.

Relative risk (RR) is the risk of the outcome in the treated group (Y) compared to the risk in the

control group (X). RR = Y / X

Relative risk reduction (RRR) is the percentage reduction in risk in the treated group (Y)

compared to the control group (X). RRR = 1 – Y / X × 100%

Absolute risk reduction (ARR) is the difference in risk between the control group (X) and the

treatment group (Y). ARR = X – Y

Numbers needed to treat (NNT) is the number of patients that must be treated over a given

period of time to prevent one adverse outcome. NNT = 1 / (X – Y)

Odds ratio (OR) is the odds of an experimental patient suffering an event compared to a patient

in the control group or the odds of risk.

Modified from Straus, S. E., Glasziou, P., Richardson, W. S., & Haynes, R. B. (2011). Evidence based

medicine: How to practice and teach it (4th ed.). Edinburgh, Scotland: Elsevier.

BOX 15-2 Definitions of Clinically Significant Statistics

1. Which of the following would be considered when appraising quantitative studies?
   (Select all that apply.)
   a. Representativeness of the sample
   b. Trustworthiness
   c. Sample size
   d. Control over extraneous variables


2. Which of the following would be considered when appraising qualitative studies? (Select
   all that apply.)
   a. Validity and reliability
   b. Audit trail
   c. Thick description
   d. Participants are experienced in the phenomenon


3. Place the following kinds of evidence in order from highest to lowest.
   a. Meta-analyses
   b. Case studies
   c. RCTs
   d. Cohort studies
   e. Expert opinions

TEST YOUR KNOWLEDGE 15-2

How did you do? 1. a, c, d; 2. b, c, d; 3. a, c, d, b, e

15.2 Appraising the Evidence 413