Deciding on the Scale Granularity of Response Categories of Likert Type Scales: The Case of a 21-Point Scale

1. IntroductionLee and Soutar (2010) maintain that while there are several ways to gather data of a quantitative nature, rating scales remain the most popular. There has been much interest recently in alternative scale formats such as graphic scales (Cook, Heath Thompson & Thompson 2001), single item scales (Lee, Douglas & Chewning 2007), tailoring scales for multicultural and/or multilingual settings (Arce-Ferrer & Ketherer 2003) and the development of individualised rating scale procedures as an alternative to researcher-defined fixed rating scales (Chami-Castaldi, Reynolds & Wallace 2008). Nevertheless, the popularity of researcher-defined scales seems to persist, and yet there seems to be relatively little attention paid by researchers to their decision to adopt a specific rating scale design.This research investigates the use a particular researcher-defined fixed rating scale, namely a 21-point Likert type scale, in the design of a questionnaire that explores factors related to staff turnover and retention. It is argued that the properties of such a scale enhance statistical analysis. The aim of this research paper is therefore to examine the use of such a scale by respondents, and by extension, to infer the usefulness of the scale for the researcher.2. Likert type scalesAccording to Rattray & Jones (2007), Likert type scales are one of a range of scale types that researchers can choose from, and they identify Frequency, Thurstone, Rasch, Guttman, Mokken and Multiple choice formats as alternatives. DeVellis (2003) refers to a Likert scale as a type of response format for a scale item, rather than a scale type. This distinction is helpful, as it serves to differentiate summated scale types from the characteristics or format of a single item. Summated scales such as the Guttman and Thurstone scales consist of a number of items making up the scale. In contrast typical response formats for a single item include the Likert, semantic differential, and visual analogue scales. This study's focus is on the response format of single items.Likert type scales can be traced back to the work in the 1930's by their namesake, Rensis Likert, who experimented with a simpler response format for various Thurstone attitude scales (Likert 1932; Likert Roslow & Murphy 1934). A statement was provided and respondents were given one of five response options by which to describe their reaction to the statement. These options were: "Agree with the statement", "Strongly agree with the statement", "Disagree with the statement", "Strongly disagree with the statement", or "Undecided". Respondents indicated their reaction by writing down a symbol that corresponded to the option, rather than writing down a number. In addition, Likert's original instructions set out the options in the order that they are listed above, and not in a more intuitively logical sequence that would suggest a continuum of reactions ranging from "Strongly disagree" to "Strongly agree". This continuum of responses has certainly become the more popular format (Dawes 2008). Furthermore, a neutral response was not provided by Likert, but rather the option of being "undecided". It is interesting to note that there is no evidence of Likert personally providing a theoretical justification of his method (Roberts, Laughlin & Wedell 1999). Nevertheless the Likert scale is seen to be consistent with classical test theory, which was developed subsequently (Roberts, et al. 1999). A Likert scale has several defining characteristics, namely a declarative statement, and a number of response categories that have distinct cut-off points and assume linearity and equal intervals between them. These characteristics are now discussed in more detail.Firstly, Likert scales consist of a "declarative sentence, followed by response options that indicate varying degrees of agreement with or endorsement of the statement. " (DeVellis, 2003 pp. …