Paola Gremigni, Department of Psychology, University of Bologna, viale Berti Pichat, 5,

Transcription

1 PRE-PRINT VERSION Validation of the Italian Modified Dental Anxiety Scale (MDAS) and invariance across gender and mode of administration Paola Gremigni 1, Nicola Mobilio 2, Giulia Casu 1, Santo Catapano 2 1 University of Bologna, Bologna, Italy 2 University of Ferrara, Ferrara, Italy Corresponding author: Paola Gremigni, Department of Psychology, University of Bologna, viale Berti Pichat, 5, Bologna, Italy. paola.gremigni2@unibo.it 1

2 Abstract About 7 12% of individuals experience high dental anxiety and it represents a barrier to to dental care. The Modified Dental Anxiety Scale (MDAS) is a brief measure of dental anxiety which is widely used in clinical practice as well as in research. The principal aims of this study were to validate the MDAS in Italy and to determine whether its validity was influenced by gender and different methods of data collection (on paper or electronically). A secondary objective was to collect further evidence of criterion validity and reliability of the scale. A self-report battery of standardized psychological measures, including the MDAS and other measures, was completed on paper by 126 patients attending a dental clinic and electronically by 108 respondents plus 40 dentists. Sixty-three percent of all subjects were female. Confirmatory factor analyses supported a one-factor model for the Italian MDAS and measurement invariance across gender and method of administration. Both internal consistency and 4-week testretest estimates of reliability were good. MDAS was shown to be differentially correlated in expected ways with other constructs. Women showed higher dental anxiety than men and online respondents reported higher dental anxiety than dental patients. Keywords: dental anxiety, validation, measurement invariance, gender differences, online survey 2

3 Introduction Dental anxiety can be defined as an adverse emotional state related to anticipated or expected encounter with a feared stimulus represented by dental treatment or certain aspects of it, such as the practice atmosphere, fear of pain, and dental drills (ter Horst & de Wit 1993). Despite improvement in preventive dentistry and advances in treatment techniques, dental anxiety shows a stable trend over the years (Smith & Heaton, 2003) and still represents a barrier to dental care (Humphris, Dyer, & Robinson, 2009). Reduction in receipt of preventive and treatment services due to dental anxiety culminates in the deterioration of oral health and oral health-related quality of life (Mehrstedt, John, Tonnies, & Micheelis, 2007). Assessment of dental anxiety is a prerequisite for building up of new knowledge about its acquisition and treatment. Self-reported questionnaires currently represent the most widely used method for this purpose, and the Modified Dental Anxiety Scale (MDAS; Humphris, Morrison, & Lindsay, 1995) is today the most used. By searching Scopus, 150 empirical studies emerged that have used the MDAS, of which 76 (50%) have been published in 2010 or later, thus attesting to the current utility of this scale. The extreme brevity and ease of self-administration of the MADS is a potential reason for its widespread use in many countries around the world as a cost-effective instrument for population-based research as well as for clinical practice. Nevertheless, despite its extensive use, validation studies of the MDAS do not always show complete and exhaustive. Validation studies of the MDAS The Modified Dental Anxiety Scale (MDAS) was modelled on the original Corah s Dental Anxiety Scale (DAS; Corah, 1969), adding a question on local anaesthesia and simplifying the response format. Sixteen validation studies of the MDAS were conducted around the world using native translations. Table 1 summarizes the psychometric characteristics of the MDAS from previous research. Insert Table 1 here 3

4 In all studies, internal consistency was assessed using Cronbach s alpha, which was acceptable to excellent. Less than half of the studies also provided evidence of test-retest reliability at one-week to three-month intervals. Structural validity was scarcely investigated: one study tested a two-factor solution with confirmatory factor analysis (CFA) (Yuan, Freeman, Lahti, Lloyd-Williams, & Humphris 2008); four studies identified a one-factor model using either explorative factor analysis (EFA) and/or CFA, whereas in the remaining studies the MDAS one-factor structure was assumed and not statistically tested. Evidence of construct validity was provided by the predicted relationships with a variety of criteria, such as dentist s ratings of dental anxiety, dental attendance, previous negative dental experiences, and other measures of dental fear and general anxiety. In Italy, the MDAS has never been validated and is sparsely used (Mobilio et al., 2012). This paper aimed to present the results of the first Italian validation study of the MDAS that investigates factorial validity, invariance across gender and mode of administration, criterion validity, and reliability. Measurement invariance (MI) was used as it examines the extent to which items or subtests have equal meaning across groups of examinees (French & Finch, 2006). In fact, except one (Yuan et al., 2008), almost all studies using the MDAS, tested gender differences using a difference-of-means method, without previously checking that the MDAS possessed comparable validity across gender. With regard to the mode of questionnaire administration, variations in the method of contacting respondents, in the mode of distributing the questionnaire, and in the way of administering the questions can affect the quality of the data (Bowling, 2005). In this study, we used MI to test the equivalence of web and paper-pencil versions of the MDAS, as the equivalence between these two modes has not been tested yet, notwithstanding that the MDAS has been administered electronically via a web page (Edmunds & Buchanan, 2012). Materials and Methods Participants 4

5 This study involved two independent samples, for a total of 234 participants: ordinary dental patients attending dental care and respondents to an online survey including dentists. One hundred twenty-six consecutive dental patients participated in the study, 34% males, aged years (M = 41.02, SD = 15.88). One hundred eight participants completed the online survey, 39.8% males, aged years (M = 34.12, SD = 10.01). Of these, 40 were dentists, 68% males, aged years (M = 44.25, SD = 11.08). The two samples significantly differed on age (F = 15.23, p <.001, η² =.06). The sample size met Gagne and Hancock s (2006) guidelines in CFA. A minimum of 200 observations was required to achieve a satisfactory convergence rate with a number of 5 indicators per factor, and minimum factor loadings of.40. Procedure We obtained permission for this study from the Ethical Committee of the Dental Clinic, University of Ferrara, Italy. The dental patient sample consisted of consecutive patients who were attending the Dental Clinic between January and December After providing written consent, patients completed the study questionnaire in the waiting room, prior to consultation. There were no refusals to participate in the study. Following the visit, the examining dentist rated each patient's anxiety and collaboration during treatment. Forty patients were randomly selected and asked to complete the MDAS again at a 4-week follow-up visit. Thirty-four completed the retest. The second sample included volunteer participants who responded the online survey, which was a non-probability web survey (Couper, 2000). Indeed, the online sample was recruited by an e- invitation sent to the workgroup members mailing lists. With the same sampling technique, a small sample of experienced dentists was recruited to test the MDAS criterion validity. All data were collected, held, and analyzed in a secure manner, and data quality was assessed by checking for completeness of responses. 5

6 Measures The MDAS was translated from English into Italian and then independently back-translated by two bilinguals following an iterative method (Guillemin et al., 1993). Any discrepancies between the two versions were resolved by joint agreement of both translators. The wording of the items and response format were tested by applying the Italian MDAS to 10 adults with low education level. No modifications were required following this pilot study. Both the paper-pencil and the online version of the survey contained: basic demographic information; a question about the use of dental services ( regular, i.e., once a year or more, or only when strictly necessary, i.e., in case of dental caries, dental pain, and other more complex and serious dental problems); a question on previous negative dental experiences, answered on a yes/no basis; the MDAS (Humphris et al., 1995), composed of 5 items asking respondents to rate their emotional reaction to the prospect of dental visits (i.e., going to the dentist for treatment and sitting in the waiting room ) and treatments (i.e., tooth drilled, teeth scaled and polished, and local anaesthetic injection ) on a 5-point scale, from 1 (not anxious) to 5 (extremely anxious); the Cognitive Behavioural Assessment form H (CBA-H; Zotti, Bertolotti, Michielin, Sanavio, & Vidotto, 2010), an Italian well-established battery of psychological tests that provides a comprehensive clinical assessment. In the present study we used only three scales: A1 (9 items) measures a general state of anxiety inspired by Spielberger s model; A2 (5 items) assesses worries and fear reactions for situations related to health management and diagnostic and curative treatments; A3 (5 items) investigates the presence of depressive thoughts. Items are answered true/false. 6

7 In the dental patient sample, the examining dentist was asked to rate the patient s dental anxiety and collaboration during treatment on a 5-point scale from 1 (not at all anxious/collaborative) to 5 (extremely anxious/collaborative). Statistical analyses Data were considered within the limits of a normal distribution if skewness and kurtosis did not exceed ± 1 (Peat & Barton, 2005). Multivariate normality was checked through the Mardia s normalized coefficient of multivariate kurtosis, with a value exceeding.5 as indicative of nonnormal multivariate distribution (Bentler, 2005). Analyses were performed in three steps. Step 1. CFA was performed to test the hypothesized one-factor model for the Italian MDAS. This model was not tested against the two-factor model proposed by Yaun et al. (2008) since two-item scales may not provide sufficient variance and cause estimation problems (Gütlin & Walach, 2007). The Maximum Likelihood method (ML) was used to estimate model parameters. Multiple goodness-of-fit indexes were used to evaluate model fit: 2 goodnessof-fit; 2/df ratio (cut-off 3; Hair Anderson, Tatham, & Black, 1998); root mean square error of approximation (RMSEA, cut-off <.08; Browne & Cudeck, 1993); comparative fit index (CFI, cut-off.95); goodness-of-fit index (GFI, cut-off.95); standardized root mean squared residual (SRMR, cut-off.08; Hu & Bentler, 1999). Two multigroup CFAs (MGCFAs) were then performed using the ML estimator to investigate invariance across groups. Progressively more constrained models were tested (Byrne & Stewart, 2006) where parameters were constrained to be equivalent across groups as follows: in Model 1 factor structure, in Model 2 factor loadings, in Model 3 factor loadings and factor variances, and in Model 4 factor loadings, factor variances, and error variances. Differences in fit between nested models were evaluated using the following parameters: 2 test, 2 (Cheung & Rensvold, 2002), RMSEA, SRMR, and CFI. Since the ² is sensitive to sample size, we set 7

8 significance level at p.001. Models were also compared using the CFI, with a value.01 as indicative of no significant decrease in fit across models (Cheung & Rensvold, 2002). Step 2. Reliability was assessed by calculating internal consistency with Cronbach s α (cutoff.70; Nunnally, 1978) and corrected item-total correlations (.30; Streiner & Norman, 2008), homogeneity with McDonald s ω-coefficient (McDonald, 1999), and test-retest with intraclass correlation coefficient (ICC; cut-off.70, Streiner & Norman, 2008). Step 3. As evidence of construct validity, zero-order correlations were calculated between the MDAS and criteria (i.e., CBA-H scales and dentist s ratings of patient s anxiety and collaboration in the dental sample). ANOVAs and relative effect sizes (small η² =.01, medium η² =.06; large η² =.14; Cohen, 1988) were computed to test the ability of the MDAS to differentiate non-dentists from dentists, participants with previous negative dental experience from those without such experiences, and regular from non-regular dental care attenders. Finally, differences on MDAS score across gender and mode of questionnaire administration were investigated using ANOVA, taking age as a covariate. Analyses were performed using SPSS 19.0 and AMOS The statistical significance level was set at.05 or.001, when appropriate. Results Factorial validity All MDAS items presented non-significant skewness and kurtosis (Table 2). Mardia s multivariate estimate of 4.09 was slightly below the limit of a non-normal multivariate distribution. Insert Table 2 here All CFA fit indices met the recommended cut-off values, indicating that the one-factor model provides a good representation of the data ( 2 5 = 10.68, p =.06; 2 /df = 2.14; RMSEA =.07; CFI =.99; GFI =.98; SRMR =.02). Examination of local fit showed that all estimated factor loadings 8

9 (Table 2) were statistically significant (p <.001). Standardized factor loadings ranged from.57 to.87 and error variances ranged between.23 and.64. Invariance across gender and mode of administration Results of MGCFAs across gender and mode of administration are summarized in Table 3. In both MGCFAs, Model 1 was supported, suggesting an invariant one-factor solution across groups. Factor loading invariance was also supported, with non-significant 2 and CFI smaller than.01 for Model 2. Model 3 did not lead to deterioration of model fit, compared to Model 2, indicating that. factor variance was comparable across gender and mode of administration. Finally, Model 4 did not provide a poorer fit than Model 3 for both MGCFAs, indicating equal residual variances across gender and mode of administration. Insert Table 3 here Criterion validity and reliability In the whole sample, MADS correlated substantially with medical fears, moderately with state anxiety, and slightly with depression (see Table 4). Using the Steiger s method (1980), MDAS had a higher correlation with medical fears (CBA-H A2) than with both depression (CBA-H A3) (p =.0003) and state anxiety (CBA-H A1) (p =.008). In the dental patient sample, MDAS correlated stronger with dental anxiety than with cooperation during treatment as rated by the dentist (CBA-H A3) (p =.006). A partial correlation analysis showed that controlling for medical fears did not lower the strength of the relationship between self- and dentist-rated dental anxiety, yet the relationship between dental anxiety and state anxiety was found to be due to levels of medical fear. Insert Table 4 here The MDAS was capable of significantly differentiating non-dentists from dentists (F = 14.07, p <.002; η² =.10), regardless of gender, age and mode of administration. Nevertheless, post-hoc comparisons (Scheffè) showed that online respondents (n = 108; M = 12.43, SD = 4.87) reported 9

10 higher dental anxiety than both dental patients (n = 126; M= 9.87, SD = 3.67) and dentists (n = 40; M = 8.33, SD = 3.77) (p <.001). In the whole non-dentist sample, previous negative dental experiences and dental care attendance were associated with MDAS, independent of age and gender, but depending upon the mode of administration (experience*mode F = 4.65, p =.03; attendance*mode F = 5.19, p =.006); therefore, the effects of these variables on MDAS were calculated separately based on the mode of administration. Among dental patients, MDAS was not associated with negative experiences, gender or age (p >.05), whereas associations between dental care attendance and MDAS depended on gender (F = 8.35, p =.005; η² =.08). Among women only, MDAS was significantly associated with attendance (F = 5.17, p =.03; η² =.08), with regular attenders (M = 9.98, SD = 2.89) showing lower dental anxiety than non-regular attenders (M = 12.28, SD = 4.55), regardless of age. Among online respondents, MDAS was significantly associated with negative experiences (F = 11.29, p =.001; η² =.10) and gender (F = 16.79, p <.001; η² =.14), but not with age. Participants with previous negative experiences (n = 49, M = 13.54, SD = 4.54) scored higher than those without such negative experiences (n = 59, M = 11.08, SD = 4.96), regardless of gender and age. MDAS was also significantly associated with dental attendance (F = 7.14, p =.009; η² =.07) and gender (F = 18.08, p <.001; η² =.15), with regular attenders (n = 40, M = 11.13, SD = 4.59) scoring lower than non-regular attenders (n = 68, M = 13.19, SD = 4.90), and. Internal consistency was good, with a Cronbach s α coefficient of.88 and corrected item-total Commento [P1]: Mancano le differenze di genere correlations in the range. Homogeneity was also good, with a McDonald s of.86. In the dentists sample, internal consistency was high, with α =.89 and item-total correlation between.55 and.83. Finally, test-retest stability over a 4-week period (n = 34) was acceptable, with an ICC of.83 (95% CI: , p <.001). Discussion 10

11 The present paper describes the Italian validation of the Modified Dental Anxiety Scale (MDAS). Our findings largely support the psychometric properties of the Italian MDAS, with the one-factor model showing adequate fit to the data, measurement invariance across gender and mode of administration, and good reliability. Construct validity based on associations with criteria was also acceptable. CFA confirmed the results of previous studies that tested the MDAS one-factor structure, and our internal consistency coefficient approached the highest values obtained in other studies (see Table 1). Test-retest replicated the results of the original study (Humpris et al., 1995), using the same 4- week interval. The MDAS was found to discriminate between dentists and ordinary people, and individuals with higher MDAS scores were rated by the dentist as more uncooperative and anxious than non-anxious patients, consistent with previous studies (Humpris et al., 1995). Negative dental experiences were confirmed to be a major antecedent for dental anxiety, and dental anxiety was confirmed to be associated with non-frequent dental attendance (see Table 1), although differently between groups. Online respondents were characterized by a pattern including higher MDAS scores, negative dental experiences and poor attendance, whereas, among dental patients, only women with higher MDAS scores also reported poor attendance. Three potential explanations might be suggested: (1) there was an online disinhibition effect (Suler, 2004), which makes people sharing personal information in cyberspace more than in the face-to-face situation; (2) computerized surveys reduce socially desirable responses, although some disagreement exists about this effect (Yun & Trumbo, 2000); (3) online respondents might actually present previous negative experiences, higher dental anxiety and poorer dental attendance, compared to patients attending dental clinics. Thus, assessing dental anxiety in patients recruited at dental clinics only may result in underestimation of dental anxiety and its antecedents/consequences. A large shared variance was observed between dental anxiety and fear of medical procedures, against a moderate shared variance between general and dental anxiety that disappeared when controlling for medical fears. This might indicate that the construct measured by the MDAS is 11

12 conceptually closer to phobic fear based on vulnerability-related cognitions (Armfield, 2010) than to situation-specific anxiety. Testing of measure invariance demonstrated that the one-factor model held well for both genders, thus allowing valid gender comparisons. Consistent with other studies (e.g., Yuan et al., 2008), women show higher dental anxiety. Such gender effects might be the result of a lower perceived capability of control in women compared with men afflicted with dental fears (Liddell & Locker, 1997). This is the first investigation to demonstrate that the factor structure of the MDAS is equivalent across mode of administration, thus allowing to use it via the web for both research and clinical purposes. The validity and reliability of online surveys have become relevant research topic due to the advantages of online data gathering (Fan &Yan, 2010). Furthermore, the number of Internet support groups for dental anxiety/phobia has risen strongly (Buchanan, Coulson, & Malik, 2010), making online assessment desirable. A limitation of this study was the significant difference in age between dental patients and online respondents, which was consistent with the fact that the population of web users is biased toward young people (Schmidt, 1997). Nevertheless, the MDAS was invariant across mode of administration and unrelated to age. In conclusion, results from this study contribute to the empirical validation of the concept of dental anxiety and support the use of the Italian MDAS by clinicians and researchers to assess dental anxiety and its change in outcome research. Declaration of Conflicting Interests The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. References 12

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18 Table 1. Psychometric characteristics of the MDAS from validation studies Country / Study Structural validity Criterion validity (Predicted relationship) Reliability UK Humphris et al., 1995 Ireland, Finland, UAE Humphris et al., 2000 Norway Haugejorden et al., 2000 UK Newton et al., 2005 Turkey Ilgüy et al., 2005 Turkey Tunc et al., 2005 China Yuan et al., 2008 None DAS, dental phobia, dental attendance, dentist s rating of patient s anxiety, cooperation, and adherence. = Test-retest (one- week) ICC =.81, (one- month) ICC =.82 None Dental attendance and nervousness about visiting the dentist. = None Dental attendance. =.89 None Self-reported state and trait anxiety. =.93 Test-retest (2-3 month) ICC =.93 None DAS. α= Test-retest (15 days) ICC=.95 None DFS (Dental Fear Survey), dental phobia, and previous α= negative experiences. Item-total correlation r= Test-retest (one-week) ICC=.74 CFA, two Dental attendance, negative affectivity, and HADS (Hospital =.74 and.86 correlated factors Anxiety and Depression Scale) anxiety. Greek None DFS, dentist s rating of patient s anxiety, and returning for a =.72 Coolidge, Arapostathis et al., 2008 second dental appointment. India None MDBS (Modified Dental Beliefs Scale) and prior unpleasant =.78 Acharya, 2008 experiences. Item-total correlation r=.83 18

19 Spain None DFS, Needle Survey (NS), and dentist s rating of patient s = Coolidge, Chambers et al., 2008 anxiety. Test-retest (1-3 week) ICC=.69 UK Humphris et al., 2009 EFA, CFA one-factor None. =.96 Romania Dumitrescu et al., 2009 None FDP (Fear of Dental Pain). =.81 Spain None MDBS, dental attendance, reason of the most recent dental =.88 Coolidge et al., 2010 visit, and caries severity. Test-retest (1-3 week) ICC=.83 Jordan EFA, CFA Dental attendance, dental anxiety, and helplessness in the =.87 Abu-Ghazaleh et al., 2011 one-factor dental surgery. Romania EFA McGill PQ (Pain Questionnaire), TAQ (Trimodal Anxiety =.90 Mărginean et al., 2012 one-factor Questionnaire), and CTS (Current Thoughts Scale). India EFA Avoidance of dental visit and VAS (Visual Analogue Scale)- =.86 Appukuttan et al., 2012 one-factor dental anxiety. Test-retest (one-week) Rho =.89 19

20 Table 2. Descriptive statistics, factor loadings, and item-total correlations of MDAS Item Mean (SD) Variance Skewness a Kurtosis b Loadings Item-total correlation* (0.98) (1.05) (1.23) (0.91) (1.19) Total (4.45) Note. a SE = 0.16; b SE = 0.32; c = adjusted Pearson s r. *All factor loadings and correlations are statistically significant at p <

21 Table 3. Fit indices for the multi-groups CFAs of the MDAS Group Model df 2 df 2 2 /df RMSEA RMSEA CI 90% SRMR CFI CFI Women vs. Men a Patients vs. Online participants b * ns ns * ns ns * ns * ns Note. a N = 234 (161 females and 113 males); b N = 234 (126 patients, 108 participants to the online survey); ns non-significant difference in 2 values; * p <.05 21

22 Table 4. Zero-order and partial correlations of the MDAS with criteria CBA-H A1 CBA-H A2 CBA-H A3 DA C (n = 234) (n = 234) (n = 234) (n = 126) (n = 126) Correlation.25**.42**.14*.40** -.18 Partial correlation controlling for CBA-H A * -.15 Note. *p <.05; **p <.01. CBA-H A1 = state anxiety, CBA-H A2 = medical fears, CBA-H A3 = depression, DA = dental anxiety rated by the dentist, C = cooperation rated by the dentist. 22