Rule of halves: implications of increasing diagnosis and reducing dropout for future workload and prescribing costs in primary care.

Evidence from one practice and from the literature suggest that approximately half of most common chronic disorders are undetected, that half of those detected are not treated, and that half of those treated are not controlled: the 'rule of halves'. Workload in primary care would increase by at least 12% if all common and important chronic disorders were fully diagnosed, treated and followed up; the accompanying effects on prescribing costs would be complex, but not necessarily inflationary. The relationship between these data and the new general practitioner contract is discussed.