Research Terms

Alternate (or parallel) forms reliability - A procedure for testing the reliability of responses to survey questions in which subjects' answers are compared after the subjects have been asked slightly different versions of the questions or when randomly selected halves of the sample have been administered slightly different versions of the questions.

Concept - A mental image that summarizes a set of similar observations, feelings, or ideas.

Conceptualization - The process of specifying what we mean by a term. In deductive research, conceptualization helps to translate portions of an abstract theory into testable hypotheses involving specific variables. In inductive research, conceptualization is an important part of the process used to make sense of related observations.

Concurrent validity - the type of validity that exists when scores on a measure are closely related to scores on a criterion measured at the same time.

Constant - A number that has a fixed value in a given situation; a characteristic or value that does not change.

Construct validity - The type of validity that is established by showing that a measure is related to other measures as specified in a theory.

Content validity - The type of validity that exists when the full range of a concept's meaning is covered by the measure.

Continuous variable - A variable for which the number represents a quantity that can be described in terms of order spread between the numbers, and/or relative amounts.

Convergent validity - The type of validity achieved when one measure of a concept is associated with different types of measures of the same concept.

Criterion validity - The type of validity that is established by comparing the scores obtained on the measure being validated to those obtained with a more direct or already validated measure of the same phenomenon.

Cronbach's alpha coefficient - A statistic commonly used to measure interitem reliability. Cronbach's alpha is the average score of all the possible split-half combinations.

Dichotomies - Variables having only two values.

Direct measure - A visual or recorded observation or a physical measure.

Discrete variable - The number assigned to a variable represents a separate category of the variable, the order of which is arbitrary.

Discriminant validity - An approach to construct validation; the scores on the measure to be validated are compared to scores on another measure of the same variable and to scores on variables that measure different but related concepts. Discriminant validity is achieved if the measure to be validated is related most strongly to its comparison measure and less so to the measures of other concepts.

Exhaustive - Every case can be classified as having at least one attribute (or value) for the variable.

Face validity - The type of validity that exists when an inspection of items used to measure a concept suggests that they are appropriate "on their face".

Factoral validity - A form of construct validity used to determine if the scale items relate correctly to different dimensions of the concept.

False positive - The participant does have a significant problem based on a screening instrument but in reality does not have the problem based on a clinical evaluation.

False negative - The participant does not have a particular problem based on a screening instrument, but the participant really does have the problem based on a clinical evaluation.

Idiosyncratic variation - Variation in responses to questions that is caused by individuals' reactions to particular words or ideas in the question instead of by variation in the concept that the question is intended to measure.

Index - A composite measure based on summing, averaging, or otherwise combining the responses to multiple questions that are intended to measure the same concept.

Indicator - The question or other operation used to indicate the value of cases on a variable.

Indirect measures - Data collected about individuals or groups without their direct knowledge or participation.

Internal consistency - An approach that calculates reliability based on the correlation among multiple items used to measure a single concept.

Interobserver reliability - When similar measurements are obtained by different observers rating the same people, events, or places.

Interval level of measurement - A measurement of a variable in which the numbers indicating a variable's values represent fixed measurements units but have no absolute, or fixed, zero point.

Intraobserver reliability - Consistency of ratings by an observer of an unchanging phenomenon at two or more points in time.

Known-groups validity - Demonstrating the validity of a measure using two groups with already identified characteristics.

Level of measurement - The mathematical precision with which the values of a variable can be expressed. The nominal level of measurement, which is qualitative, has no mathematical interpretation; the quantitative levels of measurement - ordinal, interval, and ratio - are progressively more precise mathematically.

Multidimensional scale - A scale containing subsets of questions that measure different aspects of the same concept.

Mutually exclusive - A variable's attributes are mutually exclusive when every case can be classified as having only one attribute.

Negative predictive value - The proportion of all respondents who actually do not have a particular diagnosis compared to all those who were assessed by a screening instrument as having the diagnosis.

Nominal definition - the concept is defined