Instrument-order effects: using the Oral Health Impact Profile 49 and the Short Form 12.

Whereas it is well known that the ordering of items can influence research outcomes considerably, very little literature addresses instrument-order effects. Therefore, the aim of this study was to evaluate the effect of changing the administrative order of the Short-Form-12 (SF-12) and the Oral Health Impact Profile-49 (OHIP-49). It was hypothesized that if the SF-12 was administered first, the results would show poorer scores on the SF-12 subscales, as responses would not be restrained to only the oral impacts described by the OHIP-49. Using the Mann-Whitney U-test no significant instrument-order effects were found, except for the Psychological discomfort scale of the OHIP-49, where subjects scored higher when receiving the OHIP-49 first. However, the effect size was negligible (-0.08). These results suggest that no instrument-order effects occurred. Nonetheless, more research dealing with different instruments is needed. This study was performed within a dental setting and we recommend that instrument-order effects should be studied outside this domain.

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.

On the severity of impacts captured by the dimensions of the Oral Health Impact Profile.

The Oral Health Impact Profile (OHIP), containing seven dimensions, is based on a hierarchical model. Therefore, one could argue that events described by dimensions higher in the hierarchy are judged as having a more severe impact on quality of life than events described by dimensions lower in the hierarchy. The aim of this study was to test this assumption and to assess the relative severity of impact on daily life with which each dimension is judged relative to all other dimensions. The subjects were psychology freshmen. Subjects' judgments were assessed using the method of direct ranking and the method of paired comparison. The results showed differences between dimensions, with Handicap and Psychological disability being regarded as having the most severe impact on daily life. The results demonstrated the tenability of Locker's hierarchical model as the foundation of the OHIP, in that subjects rank the dimensions in a similar order of severity as intended by this model. It is suggested that the difference of the severity of impact should be compensated for, either by including subscale weights or by increasing the number of items of subscales where the impact on Quality of Life (QoL) is judged as being more severe.