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A Likert scale (commonly pronounced "like-ert" but properly pronounced "lick-ert" ) is a psychometric scale commonly involved in research that employs questionnaires. It is the most widely used approach to scaling responses in survey research, such that the term is often used interchangeably with ''rating scale'', or more accurately the Likert-type scale, even though the two are not synonymous. The scale is named after its inventor, psychologist Rensis Likert.〔 〕 Likert distinguished between a scale proper, which emerges from collective responses to a set of items (usually eight or more), and the format in which responses are scored along a range. Technically speaking, a Likert scale refers only to the former. The difference between these two concepts has to do with the distinction Likert made between the underlying phenomenon being investigated and the means of capturing variation that points to the underlying phenomenon.〔Carifio, James and Rocco J. Perla. (2007) "Ten Common Misunderstandings, Misconceptions, Persistent Myths and Urban Legends about Likert Scales and Likert Response Formats and their Antidotes." ''Journal of Social Sciences'' 3 (3): 106-116〕 When responding to a Likert questionnaire item, respondents specify their level of agreement or disagreement on a symmetric agree-disagree scale for a series of statements. Thus, the range captures the intensity of their feelings for a given item. A scale can be created as the simple sum of questionnaire responses over the full range of the scale. In so doing, Likert scaling assumes that distances on each item are equal. Importantly, "''All items are assumed to be replications of each other or in other words items are considered to be parallel instruments''" 〔A. van Alphen, R. Halfens, A. Hasman and T. Imbos. (1994). Likert or Rasch? Nothing is more applicable than good theory. ''Journal of Advanced Nursing''. 20, 196-201〕 (p. 197). By contrast modern test theory treats the difficulty of each item (the ICCs) as information to be incorporated in scaling items. == Composition == A ''Likert scale'' is the sum of responses on several ''Likert item''s. Because many Likert scales pair each constituent Likert item with its own instance of a visual analog scale (e.g., a horizontal line, on which a subject indicates his or her response by circling or checking tick-marks), an individual item is itself sometimes erroneously referred to as a scale, with this error creating pervasive confusion in the literature and parlance of the field. A Likert item is simply a statement that the respondent is asked to evaluate by giving it a quantitative value on any kind of subjective or objective dimension, with level of agreement/disagreement being the dimension most commonly used. Well-designed Likert items exhibit : * "symmetry" in that they contain equal numbers of positive and negative positions whose respective distances apart are bilaterally symmetric about the "neutral"/zero value (whether or not that value is presented as a candidate; see the discussion of forced choice below) :and : * "balance" in that the distance between each candidate value is the same, allowing for quantitative comparisons such as averaging to be valid across items containing more than two candidate values. Often five ordered response levels are used, although many psychometricians advocate using seven or nine levels; an empirical study found that items with five or seven levels may produce slightly higher mean scores relative to the highest possible attainable score, compared to those produced from the use of 10 levels, and this difference was statistically significant. In terms of the other data characteristics, there was very little difference among the scale formats in terms of variation about the mean, skewness or kurtosis. The format of a typical five-level Likert item, for example, could be: # Strongly disagree # Disagree # Neither agree nor disagree # Agree # Strongly agree Likert scaling is a bipolar scaling method, measuring either positive or negative response to a statement. Sometimes an even-point scale is used, where the middle option of "Neither agree nor disagree" is not available. This is sometimes called a "forced choice" method, since the neutral option is removed.〔Allen, Elaine and Seaman, Christopher (2007). "Likert Scales and Data Analyses". Quality Progress 2007, 64-65. http://asq.org/quality-progress/2007/07/statistics/likert-scales-and-data-analyses.html〕 The neutral option can be seen as an easy option to take when a respondent is unsure, and so whether it is a true neutral option is questionable. A 1987 study found negligible differences between the use of "undecided" and "neutral" as the middle option in a 5-point Likert scale.〔Armstrong, Robert (1987). "The midpoint on a Five-Point Likert-Type Scale". Perceptual and Motor Skills: Vol 64, pp359-362.〕 Likert scales may be subject to distortion from several causes. Respondents may: : * Avoid using extreme response categories (''central tendency bias''), especially out of :: * a desire to avoid being perceived as having extremist views (an instance of the "social desirability bias" discussed below) and/or :: * for questions early in a test, an expectation that questions about which one has stronger views may follow, such that on earlier questions one "leaves room" for stronger responses later in the test, which expectation creates bias that is especially pernicious in that its effects are not uniform throughout the test and cannot be corrected for through simple across-the-board normalization; : * Agree with statements as presented (''acquiescence bias''), with this effect especially strong among persons, such as children, developmentally disabled persons, and the elderly or infirm, who are subjected to a culture of institutionalization that encourages and incentivizes eagerness to please; : * Disagree with sentences as presented out of a defensive desire to avoid making erroneous statements and/or avoid negative consequences that respondents may fear will result from their answers being used against them, especially if misinterpreted and/or taken out of context; : * Provide answers that they believe will be evaluated as indicating strength or lack of weakness/dysfunction ("faking good"), : * Provide answers that they believe will be evaluated as indicating weakness or presence of impairment/pathology ("faking bad"), : * Try to portray themselves or their organization in a light that they believe the examiner or society to consider more favorable than their true beliefs (''social desirability bias'', the intersubjective version of objective "faking good" discussed above); :and/or : * Try to portray themselves or their organization in a light that they believe the examiner or society to consider less favorable / more unfavorable than their true beliefs (''norm defiance'', the intersubjective version of objective "faking bad" discussed above). Designing a scale with balanced keying (an equal number of positive and negative statements and, especially, an equal number of positive and negative statements regarding each position or issue in question) can obviate the problem of acquiescence bias, since acquiescence on positively keyed items will balance acquiescence on negatively keyed items, but defensive, central tendency, and social desirability biases are somewhat more problematic. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Likert scale」の詳細全文を読む スポンサード リンク
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