Sample
A description of the population from which the survey respondents were drawn.
Sample Error
One type of inaccuracy caused by making inferences about the target population based on the sample. The sampling error is an estimate of how a sample statistic is expected to differ from the population parameter.
Sample Frame
This is the list of eligible participants included in the target population. The sample is chosen from the sampling frame.
Sample Size
This is the total unweighted count of all completed interviews.
Sample Statistic
A statistic which describes the sample. (e.g. If you want to do a survey of New York City Marathon runners, including their finishing times, the average finishing time of the those surveyed would be an example of a sample statistic. Not to be confused with population parameter, which would calculate the average finishing time of all the runners, not just a sample of them.)
Sampling
A method of selecting elements (or units) from the target population in a way that is representative. Types of sampling include: Simple random sampling, stratified sampling, systematic sampling, and multi-stage cluster sampling.
Sampling procedure
| The method by which participants in a poll were selected. |
Secondary Data
This term refers to materials and information that has previously been documented. For example, a poll, a press release, a business report.
Simple Random Sample (SRS)
The most common sampling method where each element in the population has an equal chance of being selected.
Source Document
The document from which information was gathered. In iPOLL, the source document usually refers to the topline document released by a polling organization which was used as the source for questions and topline results.
Speeding
| Respondents answering at a rate too fast to allow for adequate comprehension of questions, particularly for paper or online questionnaires. |
Split sample
| A type of survey research design in which a sample is randomly split into different groups and assigned different treatments (e.g. questions or prompts) in order to determine the effect of the treatment on survey responses. A sample may also be split into groups and asked different questions in order to maximize the number of questions that can be asked in the survey. |
Standard Deviation
A statistic that shows the dispersion of scores in a distribution of scores. It is a measure of the average amount the scores in a distribution deviate from the mean. The more widely spread out the scores are, the larger the standard deviation will be.
Standard Error (of the Mean)
A statistic indicating how much the mean score of a single sample is likely to differ from the mean score of the population. It answers the question, "How good an estimate of the population mean is the sample mean?" (Not to be confused with sampling error)
Statistic
A number that describes some characteristic of a variable. (e.g. the mean, the standard deviation)
Straightlining
| A respondent providing identical answers across a range of questions (on a printed survey, literally marking off responses in a "straight line" through the instrument). |
Stratified Sampling
A method of sampling where groups that might not otherwise be equally represented are first divided proportionately into categories (“strata”); then, a sample is randomly selected from each of these categories. (e.g. If you wanted to do a study on hospitals, you’d separate them by size—small, medium-sized, and large hospitals. From there, you would draw samples from each category so that they’d all be equally represented.
Study Note
This note field on questions in the iPOLL database pertains to the entire release, report, or study from which the question was taken.
Subject
The topic classification(s) that best describe the question. The scheme for this categorization was developed by the Roper Center and contains over 100 subject categories.
Subpopulation
A subset of the population under study. In cases where responses are not based on the entire sample, question results in iPOLL will show the Subpopulation field with a description of the portion of the sample whose responses are being reported appears here (e.g. women, or those who favor a given policy).
Survey Organization
The organization that conducted the fieldwork for a survey.
Systematic Sampling
A method of sampling where units are selected from the sampling frame by every “nth” unit. (e.g. You have a directory of 100,000 names and you want a sample of 1,000 names. Divide 100,000 by 1,000 to get 100. You will select every 100th name from the directory. Randomly select a number between 1 and 100, say 42, and select every 42nd name in groups of 100 (42, 142, 242, 342, 442.) to complete your sample.
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