Determining immunisation coverage rates in primary health care practices: a simple goal but a complex task.

PURPOSE: To explore the quality of data recording by practices and identify issues to be considered and addressed before such data can be used as a continuous measure of immunisation delivery. METHODS: One hundred and twenty-four randomly selected general practices visited to measure immunisation coverage using the various practice management systems (PMS) in use. To capture all target children it was necessary to build two queries: one generated a list of all children aged between 6 weeks and 2 years who had been to the practice- regardless of enrollment status/ the other asked dates and nature of all immunisations given. Each different PMS required a unique query to extract the necessary information. RESULTS: Variability encountered included different types and versions of PMS and operating systems/ variable degree of staff technical competence with their PMS/ proportion of enrolled children ranging from nearly 0 to 100%/ lack of consistency of the nature and location of data entry and coding/ and unreliabi