Final answer:
Mail surveys are used to collect data through the postal service; an example is the 2020 U.S. Census. They can face challenges like low response rates and unverified respondent identity, affecting data reliability.
Step-by-step explanation:
​Surveys sent to respondents using the postal service are known as mail surveys. These surveys are one of the traditional methods of collecting data, and they can be utilized to gather information from a wide and geographically spread population. A popular use of mail surveys can be demonstrated by the 2020 U.S. Census, which is a large-scale survey aiming to collect sociological data from residents of the United States and its five territories.
However, there are some challenges associated with mail surveys. Many people may choose not to respond, and when responses are received, there is no certainty of who exactly has responded, which can affect the reliability of the data. Moreover, mailing lists might not be comprehensive, which could result in a less representative sample of the target population. Surveys administered through mailings need to be designed carefully to ensure the highest possible response rate and accuracy of the data collected.