An estimate of a population parameter may be expressed in two ways:

POINT ESTIMATION A point estimate of a population parameter is a single value of a statistic. For example, 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.

INTERVAL ESTIMATION An interval estimate is defined by two numbers, between which a population parameter is said to lie.For example a < x < b is an interval estimate of the population mean μ. 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 accuracy of that point estimate by providing an interval that contains plausible values.