Estimation
The aim of sampling is usually to estimate one or more population values (parameters) from a sample. We will deal in depth with estimation in a later chapter, but mention here that estimates such as sample means or proportions are random quantities, so the estimate is not guaranteed to be the same as the value that we are estimating. We call the difference between the estimate and the population parameter being estimated the error in the estimate.
Sampling and non-sampling errors
There are two different kinds of error.
It is important to design a survey to minimise the risk of non-sampling errors. The following pages discuss various types of non-sampling error.