Table 3 Scale Development - A Global Index

(The following information is taken from 'Clinimetrics' by AR Feinstein (Feinstein, 1987))

Feinstein uses the term 'global' to refer to content which is a broad overview of a complex phenomenon. (p. 92)

"When we form a composite index or a global scale for a complex phenomenon, the scientific goal is to get an overall appraisal of the total phenomenon, not to preserve the identity of each component. If we want to know about each component, we would use or review separate indexes for the component." (p.100)

The main disadvantage of a global index is that the results are often not replicable by other observers (inter-rater reliability; reproducible consistency). However, global indexes are valuable in denoting changes of state - that is, individual ratings using the same scale will be reasonably well standardized (internal validity).

Global indices can have a high intra-rater consistency (when the same person applies it more than once, there will be standardization) but often a low inter-rater consistency (when applied by separate researchers). Since global indices permit measuring states of change, comparable results can be achieved. Further, it is possible to acquire validity in measuring since measuring change or transition ratings often yields consistency because raters are likely to use similar criteria when measuring, for example: "better, no change, worse".

Feinstein argues that "a collection of transition ratings may be reasonably well standardized within and among the individual members of the group" (p. 97). That is, if the evaluation tool created in this thesis were used to evaluate the achievement of success in priority setting in one organization, it would be possible to evaluate states of change, or to evaluate improvement.