A telephone survey is a type of opinion poll used by researchers. As with other methods of polling, their are advantages and disadvantages to utilizing telephone surveys. In statistics, a sampling error is the error caused by observing a sample instead of the whole population. The sampling error can be found by subtracting the value of a parameter from the value of a statistic.
The variations in the possible sample values of a statistic can theoretically be expressed as sampling errors, although in practice the exact sampling error is typically unknown.
In sampling, there are two main types of error: systematic errors or biases and random errors or chance errors. Random sampling is used to ensure that a sample is truly representative of the entire population.
If we were to select a perfect sample which does not exist , we would reach the same exact conclusions that we would have reached if we had surveyed the entire population.
Of course, this is not possible, and the error that is associated with the unpredictable variation in the sample is called random, or chance, error. It is not a mistake made by the researcher. Random error always exists. The size of the random error, however, can generally be controlled by taking a large enough random sample from the population. Unfortunately, the high cost of doing so can be prohibitive. If the observations are collected from a random sample, statistical theory provides probabilistic estimates of the likely size of the error for a particular statistic or estimator.
These are often expressed in terms of its standard error:. In statistics, sampling bias is a bias in which a sample is collected in such a way that some members of the intended population are less likely to be included than others.
It results in a biased sample, a non-random sample of a population in which all individuals, or instances, were not equally likely to have been selected. If this is not accounted for, results can be erroneously attributed to the phenomenon under study rather than to the method of sampling. Privacy Policy. Skip to main content. Search for:. Sample Surveys. The Literary Digest Poll Incorrect polling techniques used during the presidential election led to the demise of the popular magazine, The Literary Digest.
Key Takeaways Key Points As it had done in , , and , The Literary Digest conducted a straw poll regarding the likely outcome of the presidential election. It predicted Landon would beat Roosevelt. Roosevelt carried the 46 other states. The polling techniques used were to blame, even though they polled 10 million people and got a response from 2. They polled mostly their readers, who had more money than the typical American during the Great Depression.
Higher income people were more likely to vote Republican. Subsequent statistical analysis and studies have shown it is not necessary to poll ten million people when conducting a scientific survey. Key Terms bellwether : anything that indicates future trends straw poll : a survey of opinion which is unofficial, casual, or ad hoc. The Year the Polls Elected Dewey In the presidential election, the use of quota sampling led the polls to inaccurately predict that Dewey would defeat Truman.
Learning Objectives Criticize the polling methods used in that incorrectly predicted that Dewey would win the presidency. Key Takeaways Key Points Many polls, including Gallup, Roper, and Crossley, wrongfully predicted the outcome of the election due to their use of quota sampling.
Quota sampling is when each interviewer polls a certain number of people in various categories that are representative of the whole population, such as age, race, sex, and income. One major problem with quota sampling includes the possibility of missing an important representative category that is key to how people vote. Another is the human element involved. Key Terms quadrennial : happening every four years margin of error : An expression of the lack of precision in the results obtained from a sample.
Using Chance in Survey Work When conducting a survey, a sample can be chosen by chance or by more methodical methods. Learning Objectives Distinguish between probability samples and non-probability samples for surveys. Key Takeaways Key Points A probability sampling is one in which every unit in the population has a chance greater than zero of being selected in the sample, and this probability can be accurately determined.
Probability sampling includes simple random sampling, systematic sampling, stratified sampling, and cluster sampling. Key Terms purposive sampling : occurs when the researchers choose the sample based on who they think would be appropriate for the study; used primarily when there is a limited number of people that have expertise in the area being researched nonresponse : the absence of a response.
Even when using probability sampling methods, bias can still occur. Learning Objectives Analyze the problems associated with probability sampling. Key Takeaways Key Points Undercoverage occurs when some groups in the population are left out of the process of choosing the sample.
Response bias occurs when a respondent lies about his or her true beliefs. The wording of questions—especially if they are leading questions— can affect the outcome of a survey.
Questionnaires were actually sent to the leader of each organization. The leader was asked to distribute questionnaires to all members. Each questionnaire contained open-ended questions with many parts and follow-ups. Part of Hite's directions read as follows: "Feel free to skip around and answer only those questions you choose. It is also easy to identify that the sampling unit was an American woman. So, the key question is "What is the sampling frame? However, this answer is not correct because the sampling frame was the list from which the , who were sent the survey was obtained.
In this instance, the sampling frame included all American women who had some affiliation with an organization because those are the women that had some possibility of being contacted.
You should also remember that ideally, the sampling frame should be as close to the entire population as possible. If this is not possible, the sampling frame should appropriately represent the desired population. In this case, the sampling frame of all American women who were "affiliated with some organization" did not appropriately represent the population of all American women.
In Lesson 2 , we called this problem selection bias. Focusing on these distinctions is meant to help you think carefully about the process of creating a sample so you can identify issues that might arise in interpreting the results of a sample survey. When you read about a sample survey, always try to break down the process used into these component parts.
To get the full trends for U. Poll survey from , subscribe to Gallup Analytics. Notice: JavaScript is not enabled. Please Enable JavaScript Safely. What was the Gallup U. How were interviews conducted for the Gallup U. How many people were interviewed as part of the Gallup U. Poll: From , Gallup interviewed approximately 1, U. From , Gallup interviewed approximately U. In , Gallup interviewed approximately 1, U. For questions about how these surveys are conducted, please contact galluphelp gallup.
How Does the Gallup U. Poll Work? Text messaging is widely used in the U. Hear directly from Gallup's methodologists about our latest experiments and recommendations for conducting public opinion research. Notice: JavaScript is not enabled.
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