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Correspondence: IYDT vs NNT

Bandolier has received considerable correspondence on the use of NNTs in economic analysis. We are not sure that's the best way to use them, so a challenge to all those health economists out there - does Stephen Gray strike a chord? Is there one example where NNTs or IYDTs can be used? Any 500 word (one table) piece selected for publication gets a free Bandolier annual.


Dear Bandolier ,

I was interested to read your correspondence from Jon Brassey ( Bandolier 42 ) concerning the psychology of expressing things as a cost rather than a benefit. One simple way of calculating the priority for doing a particular intervention can be expressed as the cost of delaying the intervention divided by the amount of scarce resource required to do the intervention. This theory has been developed for use in forestry. However it could be used to compare medical interventions as well, by simply substituting '1/IYDT' (the higher the IYDT, the less useful the treatment) for the 'cost of delay'.

Thus priority could be given to interventions with a low value of IYDT x cost. These figures could be calculated as If You Do not Treat for 1 year (e.g. stick someone on a waiting list!) and the cost of treatment for one year.

It would certainly be interesting to see if some treatments, for which NNTs are known, could be compared in this way.

Yours sincerely,

Stephen Gray e-mail
Grays Pharmacy
20 Main Street
TD15 2AA

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