5.0 SURVEY ERROR and SAMPLING BIAS
survey error is the sum of the sampling error and three non-sampling errors (measurement error, non-response error, and coverage
error). Sampling errors are easier to estimate than non-sampling errors. Sampling error decreases with increasing sample size.
Non-sampling errors may be systematic like non-coverage of the whole sample or they may be non-systematic. Non-systematic
errors cause severe bias. Sampling bias, positive or negative, arises when results from the sample are consistently wrong
(biased) away from the true population parameter. The sources of bias are: incomplete or inappropriate sampling frame, use
of a wrong sampling unit, non-response bias, measurement bias, coverage bias, and sampling bias.