If samples are selected using a probability-based approach or other objective system, sampling errors tend to be compensating. The magnitude of a sampling error can be estimated from the variance of the population and the size of the sample taken. A measurement or estimate may be defined as accurate when the total error is small. This is normally a qualitative classification as there is no generally acceptable definition of a small total error. The total error includes the effects of bias and precision .
Activity Use any recent experience in measurement to make a list of possible or actual errors.
Classify these errors into their appropriate categories and estimate their likely magnitude. It may be misleading to report a measurement as an exact figure because all measurements contain error. This error means that there is a range within which the true value lies. Reporting the range within which the true value lies would avoid misleading readers about the precision of a measurement. Calculations based on these ranges would also result in ranges of values within which the true value would be expected.