Does size matter?--Evaluation of value added content of two decades of successive coding schemes in secondary care.

Over the last two decades there has been a gradual evolution from the use of simple coding schemes to controlled clinical terminologies within clinical information systems in secondary care. This evolution has required significant resources in both the development of the different coding schemes and the cost of hardware, software and human effort in implementation. During this time there has been successively larger and more complex coding schemes available for use in the UK Health Service: Read Codes 4 byte set, Read Codes 5 byte set, ICD-10 and Clinical Terms Version 3. This study evaluates what added value these successive coding schemes have offered in terms of content coverage by testing concepts derived from aClinical Information System (CIS) that has been in use to support diabetic care since 1973 (Diabeta). The schemes are quantitatively evaluated by measuring their success in providing a concept match for every notion from the CIS and their relative merits are compared. Significant added value has accrued over the years in completeness of the schemes reflected in their increased size. There appears to be justification for the continued development of clinical terminologies to support secondary care.