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On 3 Lún 2009, at 14:32, Paul Elias wrote:

This is so and my learning suggests that the 95% CI (width or precision) depends really on the sample size and the larger the sample size, therefore the increase in information/details we have about the distribution, and thus about the population parameter, and the smaller is the uncertainty about its true parameter value. The issue is that we are trying to state with a level of certainty, the probability that the true population parameter lies in the CI lower and upper limit.

The precision of a study depends on both sample size AND the variability of the measurements. The formula for the standard error of any statistic is the variability in the data divided by the amount of data. Note that the 'amount of data' isn't the sample size but the square root of the sample size, hence I've used the term 'amount of data'. 


Ronan Conroy
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Royal College of Surgeons in Ireland
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