Question

Illustrate or describe one situation where a bias sampling technique was used and why it could be considered bias. You can make one up

Answer 1

A sampling method is called biased if it systematically favors some outcomes over others. Sampling bias is sometimes called ascertainment bias (especially in biological fields) or systematic bias.

Example:

Telephone sampling is common in marketing surveys. A simple random sample may be chosen from the sampling frame consisting of a list of telephone numbers of people in the area being surveyed. This method does involve taking a simple random sample, but it is not a simple random sample of the target population (consumers in the area being surveyed.) It will miss people who do not have a phone. It may also miss people who only have a cell phone that has an area code not in the region being surveyed. It will also miss people who do not wish to be surveyed, including those who monitor calls on an answering machine and don't answer those from telephone surveyors. Thus the method systematically excludes certain types of consumers in the area.

Voluntary response samples: If the researcher appeals to people to voluntarily participate in a survey, the resulting sample is called a "voluntary response sample." Voluntary response samples are always biased: they only include people who choose volunteer, whereas a random sample would need to include people whether or not they choose to volunteer. Often, voluntary response samples oversample people who have strong opinions and undersample people who don't care much about the topic of the survey. Thus inferences from a voluntary response sample are not as trustworthy as conclusions based on a random sample of the entire population under consideration.