Aim-To assess whether diVerent classifications of neonatal care or dependency scales are comparable when used in multicentre studies of cost eVectiveness. Methods-A survey of classifications was used in a nationally representative group of 57 units in 1990-1, with a retrospective study of 10 354 cot days using patient records from a 5% random sample of 1042 admissions. Local and national classifications were correlated with medical and nursing procedures recorded for up to 26 days after each

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... ission. Results-Classifications varied substantially. Of the 57 units in our sample, 26 used one of two national classifications, sometimes modified; 17 used the Northern Neonatal Network dependency scale; and the other 14 did not record daily levels of care. In each classification, the highest level was having respiratory support by ventilation or continuous distending pressure through an endotracheal tube, nasal prongs, facemask or negative pressure device. This level of care was consistently comparable between classifications; lower levels were not. Conclusions-Retrospective comparisons between units with diVerent classifications can only reliably diVerentiate between days with and without respiratory support. There is a pressing need to develop and validate more appropriate scales for prospective multicentre studies. These should relate activity to costs and outcome.