Relative risk reduction is useful metric to standardize effect size for public heath interventions for translational research.
OBJECTIVE
Heterogeneity of effect measures in intervention studies undermines the use of evidence to inform policy. Our objective was to develop a comprehensive algorithm to convert all types of effect measures to one standard metric, relative risk reduction (RRR).


METHODS
This work was conducted to facilitate synthesis of published intervention effects for our epidemic modeling of the health impact of human immunodeficiency virus [HIV testing and counseling (HTC)]. We designed and implemented an algorithm to transform varied effect measures to RRR, representing the proportionate reduction in undesirable outcomes.


RESULTS
Our extraction of 55 HTC studies identified 473 effect measures representing unique combinations of intervention-outcome-population characteristics, using five outcome metrics: pre-post proportion (70.6%), odds ratio (14.0%), mean difference (10.2%), risk ratio (4.4%), and RRR (0.9%). Outcomes were expressed as both desirable (29.5%, eg, consistent condom use) and undesirable (70.5%, eg, inconsistent condom use). Using four examples, we demonstrate our algorithm for converting varied effect measures to RRR and provide the conceptual basis for advantages of RRR over other metrics.


CONCLUSIONS
Our review of the literature suggests that RRR, an easily understood and useful metric to convey risk reduction associated with an intervention, is underused by original and review studies.
Philip R. Lee Institute for Health Policy Studies, University of California, San Francisco, CA, USA. Electronic address: ali.mirzazadeh@ucsf.edu.
Ali
A
Mirzazadeh
Philip R. Lee Institute for Health Policy Studies, University of California, San Francisco, CA, USA.
Mohsen
M
Malekinejad
Philip R. Lee Institute for Health Policy Studies, University of California, San Francisco, CA, USA.
James G
JG
Kahn
D000465:Algorithms; D002986:Clinical Trials as Topic; D006678:HIV / Q000472:pathogenicity; D015658:HIV Infections / Q000453:epidemiology / Q000517:prevention & control* / Q000635:transmission; D006801:Humans; D015201:Meta-Analysis as Topic; D011634:Public Health; D040242:Risk Reduction Behavior; D057170:Translational Research, Biomedical
Decision making; Effect measures; Hazard ratio; Odds ratio; Relative risk reduction; Risk factor; Risk ratio