Annualized was found better than absolute risk reduction in the calculation of number needed to treat in chronic conditions.
OBJECTIVE
Recent studies have calculated number needed to treat (NNT) estimates based on annualized rates; however, the ramifications of altering the NNT statistic have not yet been explored in the literature. Here we introduce the concept of annualized NNT (ANNT), and apply it to data from randomized controlled trials (RCTs).


METHODS
Incidence rates from RCTs for serious adverse events for three medicines were compared to an older class of drugs. NNT and ANNT were calculated from the event rates for these events.


RESULTS
Based on the data, the NNT to prevent one adverse event a year vs. older medications was drug A, ANNT = 88; drug B, ANNT = 77; drug C, ANNT = 68. Equivalent calculations based on Bayesian statistics are drug C, ANNT = 54; drug B, ANNT = 49. Drug A produced a bimodal distribution, with one mode within the NNT range and the other in the number needed to harm range.


CONCLUSIONS
NNT can erroneously inflate differences between treatments when based on absolute and not differential safety. We propose that NNT be limited to acute conditions with short-term, well-defined treatment courses, and that ANNT be used for chronic conditions.
Mayne
Tracy J
TJ
Outcomes Research, Pfizer Pharmaceuticals, 235 East 42nd Street, 205/9/10, New York, NY 10017, USA. Tracy.Mayne@Pfizer.com
Whalen
Edward
E
Vu
An
A
D002908:Chronic Disease; D003627:Data Interpretation, Statistical; D064420:Drug-Related Side Effects and Adverse Reactions; D019317:Evidence-Based Medicine; D006801:Humans; D015994:Incidence; D016017:Odds Ratio; D016032:Randomized Controlled Trials as Topic; D018570:Risk Assessment / Q000379:methods; D018401:Sample Size; D013997:Time Factors