The purpose of this study was to evaluate the psychometric properties of the DAI-36 questionnaire by hybrid ordinal logistic regression (OLR/IRT) model and assess whether perceive the meaning of items in the DAI-36 questionnaire differently across gender, age and education categories.
Gender DIF analysis identified two significant uniform DIF items. This two uniform DIF items indicated females often overestimate dental anxiety than males. Regarding in items 1 and 8 of the questionnaire “I become nervous when the dentist invites me to sit down in the chair” and “I already feel uncomfortable at home when I think that the dentist will make a remark about my teeth”, in several culture, females were over-represented in physiological conditions involving anxiety, worry and fear (9, 23) This could possibly be explained by the fact that although females are more sensitive about oral health but caries tooth loss were slightly more prevalent among them (24), and they had phobia prior to dental treatment of local anaesthetic injection and tooth drilled, also they reported lower pain thresholds (1).
Gender was not a significant factor on dental anxiety in present of DIF items. To handle DIF items, there are different approaches (25) that delete items approach was used in this study, after removing two uniform DIF items, the mean dental anxiety of females and males still was not significant difference. In some previous researches, females had more dental anxiety than males (4, 6, 9, 11, 12, 26), whereas in some studies, total score of dental anxiety was not statistically significant difference between female and males that is in line with this study (1, 5, 27).
Education DIF analysis identified five significant uniform DIF items. Items 9, 20 and 21 of the questionnaire were additive uniform DIF. Although academic group overestimate dental anxiety than non-academic but these DIF magnitude were small so perceive the meaning of these items between academic and non-academic groups consistently. The total score of DAI-36 questionnaire was not statistically significant difference between academic and non-academic groups. However, after removing uniform DIF items, the mean dental anxiety of academic and non-academic was not significant difference. This is in accordance with pervious results showing level of education was not significant factor on dental anxiety (4, 5, 27–29).
This study revealed that individual with age > 30 and age < 30 respond differently to 4 items in the DAI-36 questionnaire. The considerable uniform DIF magnitude was found in items 22 and 27 of the questionnaire. The individual > 30 years old overestimate dental anxiety than < 30 years old. Regarding in item 22 of the questionnaire “In the waiting room, I sweat or freeze when I think of sitting down in the dentist's chair.”, this could possibly be explained that with increasing age compatibility is decreased and older may be have some disabilities so they reported more their anxiety of the time length of the waiting room. In a study, about 17% of adult reported exacerbated dental anxiety in the waiting room of a clinic (12).
In item 27 of the questionnaire “On my way to the dentist, I get anxious at the thought that she/he will have to drill”, it was found that older possibility concerned about many and large dental problems therefore they had more reported phobia of tooth drilled. Age was the significant factors on dental anxiety with and without DIF items, the individual greater than 30 years old had more dental anxiety than individual less than 30 years old. This could possibly be explained by older patients had referred a dentist with a bad dental experience commonly therefore their dental anxiety was higher than younger. Similar studies showed dental anxiety in patients in the 35 to 49 year was the highest (30) and in adults 31–35 years was high and decreased after 60 years old (31). In some previous studies, younger age group had the highest dental anxiety scores than older age group (11, 32) that this finding contradictory with our study.
Finally, this is the first study to evaluate DIF items of DAI-36 questionnaire across gender, age and level of education using hybrid ordinal logistic regression (OLR/IRT) model. So, other studies in different cultures can help us to insure good validity of this questions for different translations.