Many different scale formats ways of presenting answers have been tested and validated in the psychometric and marketing literature. Some of the most commonly used scales are known as the Liker scale (a 5 or 7 point balanced descriptive scale, named after Michigan Psychometric Ian Resins Liker) the Semantic Differential Scale (a 7 point bi-polar scale developed by Illinois Psychologist Charles Osgood), and the Staple Scale (a units-polar -5 to +5 scale with no neutral zero point, developed by Jan Staple of the Netherlands Institute of Public Opinion)
As the name suggests, paired comparisons require the respondent to choose one of a pair of stimuli that “has more of,” “dominates,” “precedes,” “wins over,” or “exceeds” the other with respect to some designated property of interest.
For example, six laundry detergent brands are to be compared for their “sudsiness.” Respondents are asked which one of each pair of brands has the most sudsiness. The full set of 15 paired comparisons would be considered if order of presentation is not considered).
A sample question format for paired comparisons is shown below. The order of presentation of the pairs, including which item of a pair is shown first, should be pre-determined, or can be presented randomly.
Ratings are easier and faster to administer and are analyzed as if they are interval-scaled. But, there is a risk when respondents end-pile their ratings toward the positive end of the scale. This typically happens when respondents evaluate positive constructs, such as values, that have little differentiability.
The effect is to reduce the variance of the items being rated and the ability to detect relationships with other variables. One alternative is to introduce a two-step evaluation process. Respondents first pick their most and least important values (attributes or factors) and rate them. Then, the remaining values are rated.
This procedure is used in self-explicated conjoint models and, as shown by McCarty and Shrum (2000), reduces the level of end-piling and increases the differentiation of values ratings, both in terms of dispersion and the number of different rating points used.
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