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Hi from Canada,
 
An extremely useful tool for calculating ARR and NNT from a pooled RR/OR is available for free online (VisualRx, by Chris Cates), at
http://www.nntonline.net/visualrx/
 
The tool obviates the need for hand-calculations, rightly pointed out by Andrew. Plus, the tool allows you to display the results as
an icon array. I have found this tool very helpful, for my students, as well as for my colleagues, and even for patients. It also works
quite well for convincing policy-makers about the worthiness (or lack thereof) of a new versus established interventions.
 
Cheers,
Janet
 


______________________________________________
Janet Martin, PharmD, MSc(HTA&M)
Director, Medical Evidence, Decision Integrity & Clinical Impact (MEDICI)
Assistant Professor, Department of Anesthesia & Perioperative Medicine
and Department of Epidemiology & Biostatistics
Schulich School of Medicine & Dentistry, Western University
Room B3-412, 339 Windermere Road
London, ON
Canada N6A 5A5
 
Tel: 1-519-685-8500 x34482
Email: [log in to unmask]
>>> Pablo Alonso Coello <[log in to unmask]> 2016/02/11 6:58 AM >>>

This might be helpful

 

http://www.jclinepi.com/article/S0895-4356(12)00032-7/abstract (section 8)

 

Also this one we published recently might be of interest

http://www.ncbi.nlm.nih.gov/pubmed/26560992

 

Pablo

 


Pablo Alonso Coello

Centro Cochrane Iberoamericano

Instituto de Investigación Biomédica (IIB Sant Pau)

CIBER Epidemiología y Salud Pública (CIBERESP)

C/ Sant Antoni Maria Claret 167 (Pabellón 18, planta cero)

08025 Barcelona |  España

[log in to unmask] | Skype: tartanedo

T: (+34) 93 553 78 14 | F: (+34) 93 553 78 09

De: Evidence based health (EBH) [[log in to unmask]] en nom de David Nunan [[log in to unmask]]
Enviat el: dijous, 11 / febrer / 2016 12:22
Per a: [log in to unmask]
Tema: RD/ARR & NNT from pooled RR/OR

Hi All,

Can anyone advise on calculating risk difference/absolute risk(odds) reduction (and subsequent NNT) from pooled RR/OR. I’ve seen some calculate this based on the control event rate as a product of the weighted pooled effect estimate but can’t find any lit to support this.

A worked example to illustrate:
Treatment event rate: 32/1424 = 0.022
Control event rate: 71/1546 = 0.046
Pooled OR: 0.45
RD/ARR: 0.046*0.45 = 0.021 (or 2.1%)

Is this right or wrong or somewhere horribly fuzzy in between?

Best,
David

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