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Logo of qualsafetyQuality and Safety in Health CareCurrent TOCInstructions for authors
Qual Saf Health Care. 2007 June; 16(3): 240.
PMCID: PMC2465006


Mohammed MA, Laney D. Overdispersion in health care performance data: Laney's approach. Qual Saf Health Care 2006;15:383–4.

The journal apologises for an error that has occurred within this letter, where the text following the second equation (σz  = …) should read as follows:

where N is the sum of ni and [z macron] is the mean of zi. The 3‐sigma control limits for Laney's p′‐chart are thus given by [p with macron]±3σpiσz, thereby accounting for within and between hospital variations.

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