Dear Allstaters,
I would love some help with determining an atypical number needed to treat.
I am reviewing the following article (included only for completeness):
Janet R. Casey and Michael E. Pichichero Meta-analysis of Cephalosporin
Versus Penicillin Treatment of Group A Streptococcal Tonsillopharyngitis in
Children Pediatrics 2004; 113: 866-882.
http://pediatrics.aappublications.org/cgi/reprint/113/4/866.pdf
<http://pediatrics.aappublications.org/cgi/reprint/113/4/866.pdf>
The authors are comparing cephalosporin antibiotics to penicillin
antibiotics for the cure of strep pharyngitis. The report odds ratios for
bacterial cure for each of the studies, and then a weighted summary peto
odds ratio, 3.02 (2.49, 3.67). The also report the cure rates for each
group (unweighted):
Cephalosporins 3677/3969 = 92.6 %
Penicillins 2544/3156 = 2544/3156 = 80.6%
I have found two equations for NNT, from the Centre for Evidence-based
Medicine:
The formula for converting ORs to NNTs is:
NNT = (1-(PEER*(1-OR))) / ((1-PEER)*(PEER)*(1-OR))
The formula for converting ORs to NNHs (Numbers Needed to Harm) is:
NNH = ((PEER*(OR-1))+1) / (PEER*(OR-1)*(1-PEER))
The first assumes that my treatment is good and the outcome is unfavorable,
eg. the number of treatment failures, and that my odds ratio will thus be
<1. The second assumes that my treatment is bad, and the outcome is
unfavorable, and that my odds ratio will thus be >1. I have the
circumstance where the treatment is good and the outcome is favorable. How
do I use these equations, or do I need a different equation? Since the odds
ratio is weighted, I don't think I can use the proportions to get the
appropriate odds ratio of the treatment failure.
Thank you for any ideas,
Julie
Julie Brown, MD, MPH
Pediatric Emergency Medicine, 5D-1
Children's Hospital and Regional Medical Center
4800 Sand Point Way NE, PO Box 5371
Seattle, WA 98105-0371
e-mail: [log in to unmask]
tel: (206) 987 2599
fax: (206) 729 3070
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