The dimensionality of attitude scales: a widely misunderstood idea

Summated rating scales to measure attitudes (and other human characteristics) commonly consist of numerous items whose scores are summed to yield a total score. A central assumption underlying the use of this technique is that the items in the scale reflect a common construct. If this assumption is not met, the scoring procedure produces largely meaningless, uninterpretable data. Although this important psychometric principle has been known for a long time, numerous studies in the research literature demonstrate a neglect of this principle. Some studies make no attempt at all to conceptualise the construct to be measured; others conceptualise the construct but then ignore the possibility that it may be multi‐dimensional; still others actually contain evidence which indicates that the construct is multi‐dimensional and then proceed to ignore that evidence. A possible contributor to the confusion is the widespread misunderstanding about the related yet distinct concepts of internal consistency and uni‐dimensionality. This paper presents case studies of poor and good instrument design, in the (forlorn?) hope that clarification of the issues might make a difference in the future.