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Dictionary of Evidence-based Medicine.pdf

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74 <strong>Dictionary</strong> <strong>of</strong> <strong>Evidence</strong>-<strong>based</strong> <strong>Medicine</strong><br />

Healthy user bias<br />

This is the bias which can be introduced in observational studies when<br />

one <strong>of</strong> the groups being compared consists <strong>of</strong> healthier subjects than the<br />

other(s). For example, in a number <strong>of</strong> reported observational studies <strong>of</strong><br />

hormone replacement therapy (HRT), the subjects in the HRT group appeared<br />

to have been healthier than the control group thereby possibly<br />

leading to erroneous protective effects being reported. Such a bias could<br />

be introduced by doctors, for example only prescribing HRT to healthy<br />

patients because <strong>of</strong> perceived contraindications to HRT such as the<br />

presence <strong>of</strong> cardiovascular disease (Grodstein F, Stampfer MJ, Colditz GA<br />

et al. (1997) Postmenopausal therapy and mortality. New England Journal <strong>of</strong><br />

<strong>Medicine</strong>. 336: 1769-75).<br />

Healthy year equivalent (HYE)<br />

Treatment may increase survival without necessarily improving the<br />

quality <strong>of</strong> life. Indeed, in certain instances, such as treatment with some<br />

chemotherapeutic regimens and surgical interventions in early prostatic<br />

cancer, treatment may in fact increase morbidity. How to decide on the<br />

best treatment is therefore difficult and there is a need to take account <strong>of</strong><br />

patients' preferences or utilities. The HYE associated with an intervention<br />

is the gain in life-years adjusted to take account <strong>of</strong> patients' preferences<br />

measured using a two-stage lottery approach (Mehrez A, Garni A (1989)<br />

Quality-adjusted life years, utility theory and healthy years equivalent.<br />

Medical Decision Making. 9: 141-9). While the HYE overcomes the need for<br />

assuming utility functions <strong>of</strong> the same form for all individuals and is consistent<br />

with the efficiency criterion <strong>of</strong> economic theory, it is not yet widely<br />

accepted. To date, the QALY is the favoured outcome measure <strong>of</strong> gain in<br />

cost utility analyses (Culyer AJ, Wagstaff A (1993) QALYs and HYEs.<br />

Journal <strong>of</strong> Health Economics. 11: 311-23).<br />

HEAPACT<br />

HEAPACT is an electronic link between UK health authorities and the<br />

Prescription Pricing Authority which allows the former to download<br />

computerized data about the prescribing <strong>of</strong> general practices in their areas.<br />

With HEAPACT, health authorities can obtain information about the prescribing<br />

<strong>of</strong> specific drugs in sufficient detail to, for example, identify how<br />

new drugs are being taken up by various practices (Majeed A, Evans N,<br />

Head P (1997) What can PACT tell us about prescribing in general practice<br />

BMJ. 315: 1515-19).

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