EDITOR—Rice et al present what they describe as a “needs based” formula for allocating prescribing budgets.1 This seems an improvement on the ASTRO-PU (age, sex, and temporary resident originated prescribing unit), which it replaces, but in view of its crucial impact on the resources available to general practitioners and their patients its limitations should be stated more clearly.

Despite its title, the formula does not assess need directly but relies on data from the national census to generate proxy measures. The association between these measures and prescribing costs “explains” observed variation in these costs only in the narrow statistical sense of the word. Bains and Parry,2 and Majeed3 point out further important limitations.

These criticisms are of more than academic importance. The formula is “needs based” only in a vague and general sense, but despite its manifold weaknesses there is a danger that NHS organisations will use it as …