Developing brief fatigue short forms calibrated to a common mathematical metric: is content-balancing important?

Abstract

There are clinical and research settings in which concerns about respondent burden make the use of longer self-report measures impractical. Though computer adaptive testing provides an efficient strategy for measuring patient reported outcomes, the requirement of a computer interface makes it impractical for some settings. This study evaluated how well brief short forms, constructed from a longer measure of patient reported fatigue, reproduced scores on the full measure. When the items of an item bank are calibrated using an item response theory model, it is assumed that the items are fungible units. Theoretically, there should be no advantage to balancing the content coverage of the items. We compared short forms developed using a random item selection process to short forms developed with consideration of the items relation to subdomains of fatigue (ie, physical and cognitive fatigue). Scores on short forms developed using content balancing more successfully predicted full item bank scores than did scores on short forms developed by random selection of items.

Figure 1

Correlation between short form scores and full scale scores by item selection strategy and number of items.

Figure 2

Root mean square errors (short form score minus full scale score) by item selection strategy and number of items.

Figure 3

Proportion of scores that differ from full scale score by less than 2 standard errors (based on partial credit model calibration).