Combine these for a full sample Stratified sampling is used by professional pollsters and government statisticians. Some groups have been left out of the survey. Nonresponse Those responding may have a different opinion than the nonrespondents. Sample bias Design systematically favors certain outcomes. Chance error Error due to the variability of samples.
Sample bias is the result of a poor sampling plan.
Very often the surveyor tries to get a representative sample which is an extremely poor approach. Sample bias can be eliminated using a proper sampling plan. Chance error is due to variability of samples taken. Chance error can not be eliminated but it can be made small. A stratified sampling approach is used.