Likert scales

A Likert scale (pronounced 'lick-ert') is a type of psychometric scale often used in questionnaires. It asks respondents to specify their level of agreement to each of a list of statements. It was named after Rensis Likert, who invented the scale in 1932.

Sample Question presented using a five-point Likert Scale
A typical test item in a Likert scale is a statement, the respondent is asked to indicate their degree of agreement with the statement. Traditionally a five-point scale is used, however many psychometricians advocate using a seven or nine point scale.

Ice cream is good for breakfast


 * 1) Strongly disagree
 * 2) Disagree
 * 3) Neither agree nor disagree
 * 4) Agree
 * 5) Strongly agree

Likert scaling is a bipolar scaling method, measuring either positive and negative response to a statement. Sometimes Likert scales are used in a forced choice method where the middle option of "Neither agree nor disagree" is not available. Likert scales may be subject to distortion from several causes. Respondents may avoid using extreme response categories (central tendency bias); agree with statements as presented (acquiescence response bias); or try to portray themselves or their group in a more favorable light (social desirability bias).

After the questionaire is completed the score on each item is summed together, to create a test score for the respondant. Hence, Likert scales are often called summative scales.

Scoring and analysis
Data from Likert scales are sometimes reduced to the nominal level by combining all agree and disagree responses into two categories of "accept" and "reject". The Cochran Q, or McNemar test are common statistical procedures used after this transformation.

Level of measurement
The five response categories represent an ordinal level of measurement. The categories represent an inherent order (more to less, stronger to weaker, bigger to smaller), but the numbers assigned to the categories do not indicate the magnitude of difference between the categories in the way that an interval or ratio scale would.

Rasch model
Likert scale data can, in principle, be used as a basis for obtaining interval level estimates on a continuum by applying the polytomous Rasch model, when data can be obtained that fit this model. In addition, the polytomous Rasch model permits testing of the hypothesis that the statements reflect increasing levels of an attitude or trait, as intended. For example, application of the model often indicates that the neutral category does not represent a level of attitude or trait between the disagree and agree categories.