An estimate of a population parameter may be expressed in two ways:
A point estimate of a population parameter is a single value of a statistic.
The sample mean #barx# is a point estimate of the population mean μ. Similarly, the sample proportion p is a point estimate of the population proportion P.
An interval estimate is defined by two numbers, between which a population parameter is said to lie.
#a < x < b# is an interval estimate of the population mean #mu#. It indicates that the population mean is greater than a but less than #b#.
In any estimation problem, we need to obtain both a point estimate and an interval estimate. The point estimate is our best guess of the true value of the parameter, while the interval estimate gives a measure of the accuracy of that point estimate by providing an interval that contains plausible values.