The Likert Scale was created by Rensis Likert in 1932 to measure
consumer attitudes (Edmonson, 2005). It can be used in consumer tests by
consumers respond to the degree of agreement and disagreement
statements about a product. This information is mostly used for
advertising claims on consumer perceptions about products as well as
defending any legal challenge (Lawless & Heymann, 1998). The Likert
scale was applied to many food related psychographic measurements such
as Food Neophobia Scale (Ritchey, Frank, Hursti, & Tuorila, 2003),
Food Involvement Scale (Bell & Marshall, 2003), Health and Taste
Attitude Scale (HTAS) (Roininen, et al.,
2001), List of Value Scale (Chryssohoidis & Krystallis, 2005), and
Food Related Life Style (O’Sullivan, Scholderer, & Cowan, 2005). The
challenge of using Likert scale is confusion on whether it is ordinal
or interval. This confusion causes researchers to use inappropriate
statistical methods to analyze data (Edmonson, 2005).
Responses to a single Likert item are usually treated as ordinal data.
The nonparametric tests that have been used include Wilcoxon’s signed
rank test, the Whitney-Mann-Wilcoxon test, the Kruskal-Wallis test, and
Fieldman’s test. In some cases responses to several Likert items are
summed up and treated as interval data. Researchers need to make sure
that the summed data are normally distributed. If the data are normally
distributed then the parametric statistic methods can be applied to the
summed data. However, the data transformation may be useful to make
certain that parametric assumptions are not violated (Verbych, 2007).
Parametric methods that have been proposed for analysis of ordinal data
are as follows:
- The exact probability test to use with Likert-type data was
proposed by Cooper (1976) and provided a table of critical values for
small sample size. In the case of a large sample size normal
approximation can be used but the analyst has to be careful with issues
such as: the points of the Likert scale are equally spaced, consumers
respond independently from each other, each category of scale has an
equal opportunity to get the response from consumer (Cooper, 1976).
- Using the application of ordered probit model to treat with Likert ordinal data (Daykin & Moffatt, 2002).
- Use of cumulative logits for modeling ordinal response
variables and cumulative link models for binary data (Verbych, 2007).
Bell, R., & Marshall, D. W. (2003) The construct of food involvement
in behavioral research: scale development and validation⋆. Appetite, 40
Chryssohoidis, G. M., & Krystallis, A. (2005) Organic consumers’
personal values research: Testing and validating the list of values (LOV) scale and implementing a value-based segmentation task. Food Quality and Preference, 16 (7), 585-599.
Cooper, M. (1976). An Exact Probability Test For Use With Likert-Type
Scales. Educational and Psychological Measurement, 36, 647-655.
Daykin, A. R., & Moffatt, P. G. (2002). Analyzing ordered Responses:
Areview of the ordered Probit Model. Understanding Statistic, 3,
Edmonson D.R. (2005). Likert Scale: A History. Retrieved from CHARM database.
Lawless H.T., & Haymann H. (1998) Sensory Evaluation of Food: Principle and Practices. MA: Kluwer Academic Publishers.
O’Sullivan, C., Scholderer, J., and Cowan, C. (2005) Measurement equivalence of the food related lifestyle instrument (FRL) in Ireland and Great Britain. Food Quality and Preference, 16 (1), 1-12.
Ritchey, P. N., Frank, R. A., Hursti, U., and Tuorila, H. (2003)
Validation and cross-national comparison of the food neophobia scale (FNS) using confirmatory factor analysis. Appetite, 40 (2), 163-173.
Roininen, K., Tuorila, H., Zandstra, E. H., de Graaf, C., Vehkalahti,
K., Stubenitsky, K., and Mela, D. J. (2001a) Differences in health and
taste attitudes and reported behaviour among Finnish, Dutch and British
consumers: a cross-national validation of the Health and Taste Attitude
Scales (HTAS), Appetite, 37 (1), 33-45.
Verbych, E., (2007). A Comparison of Methods to Analyze Likert Scale
Data. Unpublished master thesis, Kansas State University, Manhattan, KS.