- chance error
- sampling bias is a bias in which a sample is collected in such a way that some members of the intended population have a lower or higher sampling probability than others
- sampling errors are caused by the mere fact that only a sample, a portion of a population, is observed. For most of reasonable statistical procedures, sampling errors decrease (and converge to zero) as the sample size increases
- non-sampling errors are caused by inappropriate sampling schemes or wrong statistical techniques. Often no wise statistical techniques can rescue a poorly collected sample of data
- bias or systematic error -
individual measurement = exact value + bias + chance error:
- exact value - constant
- bias - constant
- chance error - random variable