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Logo of bmjThis ArticleThe BMJ
BMJ. 2007 April 21; 334(7598): 814.
PMCID: PMC1853174
Transparency in NICE

Construction and assumptions of models should be explicit

Tom Fahey, professor of general practice and family medicine

The National Institute for health and Clinical Excellence (NICE) uses Markov modelling, a form of decision analysis that models the effectiveness and cost effectiveness of drugs or other medical interventions in a cohort of patients over time.1 2 Construction of a Markov model relies on judgments of the likely outcomes of drug treatment, including benefits and harms.

I was asked to comment on the updated hypertension guidelines produced by NICE and the British Hypertension Society (BHS) on behalf of the Royal College of General Practitioners as part of the consultation process in spring 2006. Drug treatment for hypertension is a controversial area as guideline recommendations between the United States and the United Kingdom differ in the interpretation of recent randomised trials comparing newer and older antihypertensive agents.3

My comments related to the transparency of the Markov assumptions, including preferential modelling of diabetes as an adverse health state, failure to model differential withdrawals in different antihypertensive agents, and lack of probabilistic sampling in relation to effect size estimates for different classes of antihypertensive agents. None of these suggestions were tackled in the published report, and no comments on how the modelling and clinical guidance changed in relation to the consultation process was made. This is in marked contrast to the methods adopted by the Scottish Intercollegiate Guidelines Network (SIGN), which hosts an open meeting and incorporates consultation and peer review comments in an explicit manner (


Competing interests: None declared.


1. Maynard A. Transparency in health technology assessments: should NICE have the right to refuse access to its modelling data? BMJ 2007;334:594-5. (24 March.) [PMC free article] [PubMed]
2. Littlejohns P, Kelly M. The changing face of NICE: the same but different. Lancet 2005;366:791-3. [PubMed]
3. Psaty B, Weiss NS, Furberg CD. Recent trials in hypertension: compelling science or commercial spin? JAMA 2006;295:1704-6. [PubMed]

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