LIKERT SCALES
Likert Scales
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LIKERT SCALES
Likert Scales: Dispelling the Confusion Summary: Here's the bottom line for the busy reader. Over time and in common usage, the term, "Likert scale" has come to be applied to things far removed from its original meaning. Most importantly: • •
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A Likert scale is a multiitem scale, not a single item. A single item, regardless of its format, should not be called a Likert scale. A Likert item, which is a single item or question, should adhere to certain format requirements. An item that is merely orderedcategorical, even if it is combined with similar items in a composite scale, should not be called a Likert item or a Likerttype item. The term, discrete visual analog scale (DVAS) is more generic and an alternative in many cases. An item with ordered response levels but which has neither a Likert nor a DVAS format should simply be called an orderedcategory item. A scale composed of several orderedcategory items which are not Likert items should be referred to by the more generic name, summated rating scale.
Nature of the problem People have gradually come to use the term, "Likert scale" in very different ways. It is variously applied it to both groups of items and to single items, and in either case there is disagreement about what specific formats apply. This is a not good in general, since we would like mutually agreedon definitions. Otherwise if a researcher says, "We used a Likert scale" it isn't clear what's meant. Further, there is lack of consensus about what statistical methods are appropriate for this class of variables. This is an important matter because such variables are often used in serious applications like clinical trials. To make headway on the issue of what statistical methods are appropriate for such variables (and this is the subject of some degree of controversy), we must first agree on terms.
The Origin of Likert Scales Likert scales were originally developed by Rensis Likert, a sociologist at the University of Michigan from 1946 to 1970. Likert was concerned with measuring psychological attitudes, and wished to do this in a "scientific" way. Specifically, he sought a method that would produce attitude measures that could reasonably be interpreted as measurements on a proper metric scale, in the same sense that we consider inches or degrees Celsius true measurement scales. 2
LIKERT SCALES Other social scientists, such as Thurstone, had already developed sophisticated methods for measurement of psychological phenomena, but these were unsuited for Likert's attitude research. Likert, after trying various alternatives, gradually developed what we now call Likert scales. Likert used a number of specific techniques to first generate items, and then select from among them those that were valid, unidimensional (all measuring a common trait), and well discriminating. For example, he sometimes used judges to rate items' quality or content. All of these methods collectively go into what is formally called Likert scaling. Without failing to appreciate Likert's contributions to the science of scaling, we use the term "Likert scale" in a somewhat broader sense here to include basically any scale composed of Likert or Likerttype items. That is, we distinguish between Likert scaling and Likert scales, the former term being more specific. (We thereby avoid having to introduce yet another category, Likerttype scales.) Once constructed, Likert's scales had a format like this: Please indicate how much you agree or disagree with each of these statements: Neither agree Strongly Somewhat nor Somewhat Strongly disagree disagree disagree agree agree -------------------------------------------------------------------The president is 1 2 3 4 5 doing a good job. The Congress is doing a good job.
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The Secretary of Defense is doing a good job.
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Example 1. A Likert scale
Here the construct being measured might be attitude towards American politics. By Likert's method, a person's attitude is measured by combining (adding or averaging) their responses across all items. This summing or averaging across several items was essential for Likert to contribute to genuine measurement. We note several characteristics or features that define a Likert scale: 1. 2. 3. 4.
The scale contains several items. Response levels are arranged horizontally. Response levels are anchored with consecutive integers. Response levels are also anchored with verbal labels which connote moreorless evenlyspaced gradations. 3
LIKERT SCALES 5. Verbal labels are bivalent and symmetrical about a neutral middle and 6. In Likert's usage, the scale always measures attitude in terms of level of agreement/disagreement to a target statement (but see below) Criterion 5 usually means there is an odd number of response levels. Typically the number is 5, though sometimes 7, 9, or 11 levels are used. Only a scale with all these characteristics might qualify as a genuine Likert scale. We probably don't want to be that strict, however. In particular, it seems reasonable to apply Likert's methodology to domains other than attitude measurement. The view recommended here is that features 14 above comprise the main requirements for what can be accurately termed a Likert scale. This much said, we now address two of the biggest and most common confusions people make. First: Common Error 1 A Likert scale is never an individual item; it is always a set of several items, with specific format features, the responses to which are added or averaged to produce an overall score or measurement. A single item, even if formatted exactly as one of Likert's items, is not a Likert scale. The confusion is understandable, however, since each item of a Likert scale itself has scale like appearance. But these are definitely to be distinguished from the Likert scale proper, which is made up of the entire set of items.
Likert items The question then arises: so what *should* we call single items of this kind? Is there a term by which we may distinguish them from other kinds of items, such as ordinary multiple choice ones? If features 2 through 5 above are all present, we may justifiably call them Likert items. If only 2 through 4 are present, we might call them Likerttype items instead. How do you feel about the President's performance in domestic affairs?
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LIKERT SCALES Strongly disapprove
Somewhat disapprove
Neutral
Somewhat approve
Strongly approve
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Example 2: A Likert item
Consider the example above. Here we meet all criteria 2 5. It seems fair to call this a Likert item, even though it doesn't refer to agreement/disagreement to a target statement. How far can we legitimately broaden the definition? This is a judgment call on the part of the researcher. It is this writer's opinion that only criterion 5that the anchor labels be bivalent (distinctly twodirectional) and symmetricalmay be relaxed, and then this produces a Likert type item. Without conditions 24 the item is basically not Likerttype in any sense. The following, then, would be considered a Likerttype item. How often do you go out to see a movie? Never
Sometimes
Average
Often
Very often
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Example 3: A Likerttype item
Here the response levels are not bivalent: the lower terminus is merely "Never". There is no exact opposite of "Very often". Yet the categories are reasonably interpretable as evenly spaced, especially when associated with consecutive integers in an evenlyspaced printed format. The label for level 3, "Average" clearly denotes centrality of this response category. Similarly, we seem reasonably justified in permitting an even number of response levels, and, along with this, that there not be an exact middle or neutral categoryprovided the other criteria are maintained. There are shades of gray here, so it is difficult to provide a universally applicable set of rules. But certainly the further away an item is from the criteria shown, the less inclined one should be to refer to it as a Likert item or Likerttype item. In particular, most regrettable is the tendency, not uncommon today, to refer to any ordered category item as Likerttype. We may treat this kind of error rather summarily, as follows: Common Error 2 This is not a Likert-scale, a Likert item, or a Likert-type item:
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LIKERT SCALES How often do you smoke cigarettes? 1. 2. 3. 4.
Never Once in a while 1-5 per day More than 5 per day.
This is simply an item with ordered response levels, or an orderedcategory item. This is so even if the item is one of several that will be combined to form an aggregate scale. In this case, one simply has a summated rating scale comprised of several orderedcategory variables.
Discrete visual analog scales Increasingly, and especially on the web, we see items with a format like this:
How helpful did you find this software? Not helpful
Helpful
1234567 Example 4. A discrete visual analog scale
or even this: How helpful did you find this software? Not helpful
Helpful Example 5. A second discrete visual analog scale
Note that several of our criteria are missing here. In particular, there are no verbal labels at all, except to define the poles of a continuum. Example 4 corresponds to what is called a semantic differential item.
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LIKERT SCALES The recommendation here is that items of either type above should be called simply discrete visual analog scale (DVAS) items. Such an item is a visual analog scale, because the printed format implies specific metric relations among the response levels. It is discrete because only prespecified levels may be given by the respondent; this is in contrast with a more general visual analog scale format, where, for instance, the respondent may be instructed to place a mark on anywhere on a line to indicate his or her level of response. Note that DVAS is a more generic term than "Likerttype item", and superordinate to it. All Likerttype items, at least according to the view here, are DVAS, but all DVAS are not Likert type items. Some might suggest that the essential innovation, and, from this, the defining feature, of a Likert scale was not so much the item format, as that the responses of several items were added or averaged to produce a composite score; f further, as this is an important and common technique, some name is needed. Here we simply note that there is an alternative name for such multiitem scales, namely summated rating scales. Multiitem scales, where individual items lack the features listed above, should be called this or something equivalent, and not Likert scales. Web: http://ourworld.compuserve.com/homepages/jsuebersax/likert.htm Web: http://recepozcan06.blogcu.com/
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