Confidence intervals

Confidence intervals provide a range of values within which we are fairly certain (97.5% certain) that the true underlying rate or relative risk for that trust lies, taking account of random variation.

This range is required as there is likely to be some variation that occurs by chance. With 97.5% per cent confidence intervals, the real value (for example the standardised mortality ratio or SMR which is used to compare death rates) will fall somewhere between the values of the two confidence limits 97.5 times out of 100.

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