ABSTRACT
Any estimate that we make of the value of a population parameter (such as the mean length) should be accompanied by an estimate of its variability — the
standard error
. As we have seen in Chapter 1, we can say that there is a 68% chance that the population mean will lie within one standard error of the sample mean of any sample that has been taken correctly. This range is called a
confidence interval
. However, we usually want to be rather more confident than only 68%. The greater the chance of our range containing the population mean, the wider the confidence interval must be.
