Non-response is a source of error in surveys that appears when part of the data to be collected are not observed. It has the potential to bias significantly the results of the survey and, consequently, to prevent valid inference.Non-response reduces the sample size, and therefore increases the variance of estimators, leading to larger margins of error.A more serious effect of non-response is that it can be selective. This occurs if, due to non-response, specific groups are under- or over-represented in the survey. To say it in other word: estimates are significantly too high or too low.There...