The deputy chief executive of the NHS standards watchdog has insisted that having one nurse to every eight patients is not a "magic number".
Gillian Leng of the National Institute for Clinical Excellence told ITV News that in many cases, such as in intensive care units, nurses should be caring for much fewer than eight patients at a time.
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The storms that struck Texas and Oklahoma late on Tuesday brought tornadoes, tennis ball-sized hail and powerful winds.
Samantha Baldwin, 42, and her sons Louis Madge, nine, and Dylan Madge, six, haven't been seen for two days.
A spokesman for the UK Coastguard said it was coordinating a search operation in the Caernarfon Bay area of North Wales.