Item-order effects in the Oral Health Impact Profile (OHIP)

Items and subscales in quality of life questionnaires generally have a part-whole combination, making the content of one item more general than another. Consequently, order effects can occur. The aim of this study was to evaluate the effect of changing the item order of the Oral Health Impact Profile (OHIP). Two versions of the OHIP were randomly distributed amongst psychology freshmen. Subjects who filled out the version in which more general items were presented first showed higher subscale scores. Using the Mann-Whitney U-test, small, but statistically significant, differences between the two versions of the OHIP were found on the Psychological disability scale, the Social disability scale, and the Handicap scale. Subscale intercorrelations of both versions of the OHIP were compared to investigate whether item order also influences the factor structure. Statistically significant differences between subscale intercorrelations were found, indicating a different factor structure for both versions. In conclusion, the OHIP seems to be susceptible to order effects, implying that the original item order of the OHIP should be upheld, especially when considering comparing research outcomes with other studies.