# Likert Scale Analysis

What are some interesting techniques that can be used to analyze Likert data?

As a frame of reference, I have constructed a survey with about 50 items which are intended to assess the attitudes of the survey participants towards two very broad categories. Each item is on a 5 point scale.

The survey will be offered multiple times, thus pre and post testing is possible, although not necessarily the aim of the survey.

• There are numerous threads here on Likert data. Did you look at any of them? Commented Nov 13, 2013 at 19:19
• what is the relationship between your items? Do you intend to construct test scales or is this an eploratory study?
– jank
Commented Nov 13, 2013 at 19:56
• Nick Cox, I looked through many of the Likert data threads. They were more specific to a particular problem. I wanted a more general response to Likert analysis. jank, Half of the items relate to one broad category and half to the other. I do not intend on constructing scales this is more exploratory. Thanks for your feedback! Commented Nov 13, 2013 at 21:10
• Essentially any book on ordinal modelling gives a very full answer. See e.g. amazon.com/Analysis-Ordinal-Categorical-Probability-Statistics/… Commented Nov 13, 2013 at 21:42

It looks like you want to do something like principal component analysis and find out two components from these 50 items. A very good technique for Likert data will be conducting Non-linear Principal Component Analysis or Categorical PCA instead of usual PCA. Papers have shown that it works better than usual PCA for ordinal data.

Key papers are from Jacqueline J. Meulman, see e.g. Nonlinear principal components analysis: Introduction and application (Psychol Methods. 2007 12(3):336-58) or PCA with nonlinear optimal scaling transformations for ordinal and nominal data (SAGE Handbook of Quantitative Methodology for the Social Sciences, 2004).

Tests involving the multinomial will be useful for you if you want to examine the distribution of Likert scores. From what I recall, Likert data are ordinal, not interval/ratio. Therefore, many nonparametric tests will be helpful, for example:

1. Wilcoxon signed ranks for tests of central tendency
2. Mann-Whitney U test to compare two medians
3. Siegel-Tukey test for variabilty
4. Kruskal-Wallis nonparametric ANOVA for independent samples
5. Friedman two-way analysis of variance for dependent samples

Likert questions can be analyzed individually or simultaneously. When analyzed individually, one can use a non-parametric test (Mann-Whitney U) to compare the proportions of two groups. One can use Kruskal-Wallis to test for more than two groups.

However, more commonly likert questions can be combined into multiple ranking questions, like:

The questions can be analyzed simultaneously with a non-parametric paired test, such as the Wilcoxon signed-rank test. The data is paired because a respondent be an Asian and might not like any kind of fast-food restaurant, whereas a US respondent would be morel likely to pick "High" for Burger King and McDondal's.

We can use the signed-rank test to answer question such as: Is McDonald more favourable than Burger King. This is like comparing proportions.

As @Pablo Bernabeu says, ordinal principle components analysis (PCA) is one option. Though, there are other methods you could use to look for "two broad categories" underlying your 50 items. The first is exploratory factor analysis (EFA) with ordinal data, and the second is item factor analysis (IFA, which factor analysis for item level data). See Wirth & Edwards (2007) for more information on these methods.

References

Wirth, R. J., & Edwards, M. C. (2007). Item factor analysis: current approaches and future directions. Psychological methods, 12(1), 58.