Article Text
Correction
CORRECTIONS
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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 z̄ is the mean of zi. The 3-sigma control limits for Laney’s p′-chart are thus given by p̄±3σpiσz, thereby accounting for within and between hospital variations.