Can Likert scales be considered interval?
Likert scales (ex., strongly agree, agree, etc.) are very commonly used with interval procedures, provided the scale item has at least 5 and preferably 7 categories. Most researchers would not use a 3-point Likert scale with a technique requiring interval data. The fewer the number of points, the more likely the departure from the assumption of normal distribution, required for many tests. Here is a typical footnote inserted in research using interval techniques with Likert scales: “In regard to our use of (insert name of procedure), which assumes interval data, with ordinal Likert scale items, in a recent review of the literature on this topic, Jaccard and Wan (1996: 4) summarize, “for many statistical tests, rather severe departures (from intervalness) do not seem to affect Type I and Type II errors dramatically (Jaccard & Wan, 1996). Likert scales are ordinal but their use in statistical procedures assuming interval level data is commonplace for the reason given above. Note, though,
