A | B | C | D | E | F | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Z

Incidence - The percentage of the population or group that qualifies for inclusion in the sample using some criteria.

Independent Samples t-test - Used to compare the means and check for significant differences between the means of two independent samples.

Inferential Statistics - Concerned with the mathematical techniques that allow the use of collected sample data to be generalized to the population.

Information - Data that has been converted into a meaningful and useful context for the receiver.

Information Control - Term applied to studies using questionnaires and concerning the amount and accuracy of the information that can be obtained from respondents.

Instrument Variation - Any and all changes in the measuring device used in an experiment that might account for differences in two or more measurements.

Internal Validity - One criterion by which an experiment is evaluated; the criterion focuses on obtaining evidence demonstrating that the variation in the criterion variable was the result of exposure to the treatment or experimental variable.

Internet Samples - Classified as unrestricted, screened, and recruited. In unrestricted Internet samples, anyone who desires can complete the online questionnaire. Screened Internet samples impose quotas based on some desired sample characteristics and screen respondents before presenting the questionnaire. Recruited Internet samples recruit respondents in targeted populations by phone, mail, e-mail, or in person before directing qualified participants to the online questionnaire.

Interquartile Range - The distance between the upper and lower quartiles.

Interval Scales - Have the attributes of magnitude and equal intervals. Each unit represents the same magnitude of the variable being measured across the whole range of the scale. Also, zero is an arbitrary point on the scale, which means that comparisons about how many times greater one score is than another cannot be made. Scoring on IQ tests and most standardized tests are measured on interval scales. An example of an interval scale is an attitudinal scale of agree/disagree ranked responses: strongly disagree, disagree, neither agrees nor disagrees, agree, and strongly agree.

Item Nonresponse - Source of nonsampling error that arises when a respondent agrees to an interview but refuses or is unable to answer specific questions.

Itemized Rating Scale - Scale in which individuals must indicate their ratings of an attribute or object by selecting one from among a limited number of categories that best describes their attitude toward the attribute or object.