Likert Scale: Misuse of Mid-Point Anchor

Abstract

Validity of responses to surveys is affected by how respondents interpret the items and the anchors used in the rating scale. We show that under some circumstances, the mid-point anchor of the traditional 5-point Likert scale could be interpreted as a non-substantive response reflecting a lack of knowledge answer. An effective way to encourage respondents to read the mid-point anchor as a point representing their attitude in the middle of the continuum–is to provide a “Don’t Know” option at the end of the rating scale with a gap to indicate that it is a non-substantive response option.

Key Words: Likert Scale, Survey, Scale Construction

Likert Scale: Misuse of Mid-Point Anchor

Surveys have long been recognized as an efficient method to gather opinion or factual information and to assess attitudes for large numbers of respondents (Tourangeau, Rips, & Rasinski, 2000). Decades ago, different scaling methods, such as Likert, Thurstone, Guttman, and Semantic Differential, were developed to measure attitude. According to Carifio and Perla (2008):“Likert methodology is one of the most commonly used methodologies in all fields of research, but particularly so in allied health, medicine and medical education” (p.1151).

In Likert’s (1932) original formulation, the rating scale consisted of five points with “agree” and “disagree” labels on which the respondent indicated direction and intensity of agreement with declarative statements. In 2004, Jamieson echoed the first of the “seven deadly sins of statistical analysis” presented by Kuzon et al. (1996) and argued that use of a Likert scale yields data that are ordinal and hence parametric statistics should not be used to analyze these data. Since then, strong reactions from researchers have refuted her “ordinalist” view on Likert scale data analysis. (Pell, 2005; Carifio & Perla, 2007, 2008; Norman, 2010). [Her response to critics was published in 2005 in the same journal.]

The counter-argument is, even though the Likert scale format yields ordinal item responses, the derived scale scores are interval, and, even if ordinal, as long as there are 4 to 8 items per scale or subscale and 5 to 7 anchors points are used (Carifio & Perla, 2007), parametric statistics can still be applied because parametric tests are robust. The debate appears to have been settled in favor of the “intervalist” position. Norman (2010) declared: “Parametric statistics can be used with Likert data, with small sample sizes, with unequal variances, and with non-normal distributions, with no fear of ‘coming to the wrong conclusion.’ These findings are consistent with empirical literature dating back nearly 80 years. The controversy can cease (but likely won’t).” No response from the “ordinalists” has been heard since. In this paper, we put forth another often ignored problem in the use of the Likert scale.

Despite the controversies about the Likert scale, two issues all researchers have agreed on are (1) anchors must be chosen so they are roughly equidistant on the continuum underlying attitude being measured, and (2) the selection of an anchor must be a substantive response, a unit of information reflecting a point on the continuum.

Theoretically, every abstract construct exists on an underlying continuum. Discrete anchor points along the continuum are often provided for respondents to choose from. Choice of anchors in an attempt to create an equal interval rating scale has been researched for over three decades (e.g., Lam & Klockers, 1982). In addition to subjective judgment of the intensity of various anchors, through a rank ordering procedure, “agreement,” “evaluation,” and “frequency” anchors have been scaled. The derived numerical indices show the positions of the anchors on the underlying continuum to assist researchers in “choosing equally spaced response categories for summated rating scales” (Spector, 1976, p.374).

Likert used the five anchors: “strongly agree,” “agree,” “neither agree nor disagree,” “disagree,” and “strongly disagree.” Since then, the middle anchor has been variously labeled as “Neutral” (Armstrong, 1987), “Undecided,” (Armstrong, 1987; Lock, 2001), “Uncertain” or “not sure,” (Klopfer & Madden, 1980) and “?” (DuBois & Burns, 1975; Klopfer & Madden,1987).11In a dissertation read by the first author, “don’t know” was used as the mid-point anchor. In all of these cases, the distance between the mid-point anchor and the two adjacent anchors, “agree” and “disagree,” seems the same. However, it is not clear if all these middle anchors are interpreted by respondents as an attitude with intensity at the middle of the agreement-disagreement bipolar continuum and not used as “don’t know” (DK). Under some circumstances, the mid-point response to an item could be a non-substantive response reflecting a lack of knowledge answer. When such an item response is scored and included in the computation of the scale or sub-scale score, validity of the aggregated score suffers. We believe that this error has occurred but is typically undetected in survey research. The focus of this paper was to review the potential misuse of the middle anchor of the Likert scale and offer a strategy to minimize this potential misuse.