Jacobien M. Kieffer

Linking oral health, general health, and quality of life

The aim of this work was to assess the association among oral health, general health, and quality of life (QoL). The Oral Health Impact Profile (OHIP-49) and the RAND-36 were distributed amongst 118 psychology freshmen. Additionally, two single items self-rated general health (SRGH) and self-rated oral health (SROH) - were administered. Kruskal-Wallis and Mann-Whitney U-tests were used to evaluate differences between SRGH and SROH categories, regarding OHIP subscale scores and RAND subscale scores. More than 75% of the subjects rated their oral and general health as good. Mean OHIP scores and RAND scores indicated a relatively good oral- and general health-related QoL respectively. The correlation between oral and general health was weak. Significant differences were found between SRGH categories regarding RAND subscale scores, except for the role emotional and mental health subscales. Significant differences were also found between SROH categories regarding OHIP subscale scores, except for the psychological disability subscale. However, no significant differences were found between SRGH categories regarding OHIP subscale scores, or between SROH categories regarding RAND subscale scores. The findings suggest that oral health, general health, and QoL have different determinants. Furthermore, oral health and general health appear to be mostly unrelated in this seemingly healthy population. It is proposed that if no apparent disease is present, oral and general health must be regarded as separate constructs.

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.

Model specification in oral health-related quality of life research

The aim of this study was to analyze conventional wisdom regarding the construction and analysis of oral health-related quality of life (OHRQoL) questionnaires and to outline statistical complications. Most methods used for developing and analyzing questionnaires, such as factor analysis and Cronbachs alpha, presume psychological constructs to be latent, inferring a reflective measurement model with the underlying assumption of local independence. Local independence implies that the latent variable explains why the variables observed are related. Many OHRQoL questionnaires are analyzed as if they were based on a reflective measurement model; local independence is thus assumed. This assumption requires these questionnaires to consist solely of items that reflect, instead of determine, OHRQoL. The tenability of this assumption is the main topic of the present study. It is argued that OHRQoL questionnaires are a mix of both a formative measurement model and a reflective measurement model, thus violating the assumption of local independence. The implications are discussed.

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.

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 Lockers 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.