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Two errors occurred in this regular review by J I Tay and colleagues (1 April, pp 916-9). The y axis of figure 3 was incorrectly labelled: the concentration should have ranged from 50 to 550 (not 500-5500) IU/l. The reference in the caption to figure 3 should read: “Braunstein et al 1976 [not 1996].”
