UK Population Norms for the Modified Dental Anxiety Scale
UK Population Norms for the Modified Dental Anxiety Scale
The psychometrics for the sample are provided in Table 1 including the means and standard deviations for each question response, internal consistency coefficient (Cronbach's alpha) with 95% confidence intervals, and the results of confirmatory factor analysis (CFA) which were inspected for the unidimensional solution. Indices of fit include chi-square, CFI, TLI and RMSEA. Factor weightings between the latent variable and individual items are displayed including maximum-likelihood, and asymptotic distribution free estimates for comparison purposes. Note that 3 error covariances were specified. The internal consistency coefficient of 0.917 is regarded as 'excellent'. The sample size of this study is sufficient to show narrow confidence intervals. The scale can be considered to be unidimensional as shown by the CFA and the indices of fit lying well within conventional limits of acceptability. This was reflected in the near identical factor loadings obtained from maximum likelihood or distribution free estimation methods.
The total MDAS scores were found to vary significantly by the independent factors of gender, age, self-reported regularity of dental attendance and social status (Table 2). Females showed greater dental anxiety than men (F = 533.18, df = 1, 10084, p = 0.0001), a decreasing level with age category (overall F = 53.86, df = 6, 10079, p = 0.0001, linear effect: F = 293.35, p = 0.0001, quadratic effect: F = 18.01, p = .0001), increase with less regular visiting (F = 244.26, df = 2, 10083, p = 0.0001) and a weaker but significant effect of social status (F = 15.64, df = 6, 10079, p = 0.0001). On exclusion of the mixed category: the long term unemployed and unclassified, in the social status classification, the effect of social status on dental anxiety was linear (F = 25.12, p < .0001) and the degree of non-linearity was borderline non-significant (F = 2.40, p = 0.065). Prior to the exclusion of this mixed category the p levels, for the linearity testing, were 0.15 and .001 respectively.
The percentile ranks for MDAS raw scores can be obtained using Table 3, Table 4, Table 5, Table 6, Table 7, Table 8. As gender and age both influenced MDAS scores appreciably, the normative data were stratified by both these variables; three age bands were created (16 to 34, 35–54, 55+). The age bands were chosen as they conformed to the 3 bands reported in the ADHS report. In addition to providing the point estimates of the percentile ranks, the tables also provide 95% interval estimates. An expanded age breakdown (4 or more bands) was not selected as the percentile confidence intervals would become too large for practical interpretation. The overall mean levels of dental anxiety in the current survey (10.65, SD 5.55) and the previous 2008 survey report (10.39, SD 5.46) was not significantly different (p = 0.16). This was demonstrated further when these means were adjusted for gender, age bands and social status classification (current study: mean = 10.61, 95% CIs 10.50, 10.73; 2008 report: mean = 10.50, 95% CIs 10.11, 10.89; F = 0.31, df (35, 10245), p = 0.58).
As previously noted, a compiled (i.e. ready-to-run) computer program for PCs, MDAS_PRs.exe, was written (using the Delphi programming language) to express a patient's raw score on the MDAS as a percentile rank with accompanying interval estimate (the program will also run on a Mac provided that suitable PC emulation software is installed). The program is free and can be downloaded (either as an uncompressed executable or as a zip file) from the first author's web pages at http://medicine.st-andrews.ac.uk/supplemental/humphris/dentalAnxiety.htm, or from http://homepages.abdn.ac.uk/j.crawford/pages/dept/MDAS_PRs.htm (After downloading the program it can be run by clicking on the program in windows explorer, or, if a shortcut to the program has been created on the user's desktop, by clicking on the shortcut icon).
The program prompts the user to select the patient's gender and age using radio buttons and to enter their MDAS raw score. The output from the program consists of the patient's raw score on the MDAS (as entered by the user), and the point and interval estimates of the percentile rank for the score. These results can be viewed on screen, saved to a file, and/or printed.
Results
Scale Psychometrics
The psychometrics for the sample are provided in Table 1 including the means and standard deviations for each question response, internal consistency coefficient (Cronbach's alpha) with 95% confidence intervals, and the results of confirmatory factor analysis (CFA) which were inspected for the unidimensional solution. Indices of fit include chi-square, CFI, TLI and RMSEA. Factor weightings between the latent variable and individual items are displayed including maximum-likelihood, and asymptotic distribution free estimates for comparison purposes. Note that 3 error covariances were specified. The internal consistency coefficient of 0.917 is regarded as 'excellent'. The sample size of this study is sufficient to show narrow confidence intervals. The scale can be considered to be unidimensional as shown by the CFA and the indices of fit lying well within conventional limits of acceptability. This was reflected in the near identical factor loadings obtained from maximum likelihood or distribution free estimation methods.
Variation of Dental Anxiety
The total MDAS scores were found to vary significantly by the independent factors of gender, age, self-reported regularity of dental attendance and social status (Table 2). Females showed greater dental anxiety than men (F = 533.18, df = 1, 10084, p = 0.0001), a decreasing level with age category (overall F = 53.86, df = 6, 10079, p = 0.0001, linear effect: F = 293.35, p = 0.0001, quadratic effect: F = 18.01, p = .0001), increase with less regular visiting (F = 244.26, df = 2, 10083, p = 0.0001) and a weaker but significant effect of social status (F = 15.64, df = 6, 10079, p = 0.0001). On exclusion of the mixed category: the long term unemployed and unclassified, in the social status classification, the effect of social status on dental anxiety was linear (F = 25.12, p < .0001) and the degree of non-linearity was borderline non-significant (F = 2.40, p = 0.065). Prior to the exclusion of this mixed category the p levels, for the linearity testing, were 0.15 and .001 respectively.
Obtaining Point and Interval Estimates of the Percentile Ranks for Raw Scores
The percentile ranks for MDAS raw scores can be obtained using Table 3, Table 4, Table 5, Table 6, Table 7, Table 8. As gender and age both influenced MDAS scores appreciably, the normative data were stratified by both these variables; three age bands were created (16 to 34, 35–54, 55+). The age bands were chosen as they conformed to the 3 bands reported in the ADHS report. In addition to providing the point estimates of the percentile ranks, the tables also provide 95% interval estimates. An expanded age breakdown (4 or more bands) was not selected as the percentile confidence intervals would become too large for practical interpretation. The overall mean levels of dental anxiety in the current survey (10.65, SD 5.55) and the previous 2008 survey report (10.39, SD 5.46) was not significantly different (p = 0.16). This was demonstrated further when these means were adjusted for gender, age bands and social status classification (current study: mean = 10.61, 95% CIs 10.50, 10.73; 2008 report: mean = 10.50, 95% CIs 10.11, 10.89; F = 0.31, df (35, 10245), p = 0.58).
Computer Program for Scoring the MDAS
As previously noted, a compiled (i.e. ready-to-run) computer program for PCs, MDAS_PRs.exe, was written (using the Delphi programming language) to express a patient's raw score on the MDAS as a percentile rank with accompanying interval estimate (the program will also run on a Mac provided that suitable PC emulation software is installed). The program is free and can be downloaded (either as an uncompressed executable or as a zip file) from the first author's web pages at http://medicine.st-andrews.ac.uk/supplemental/humphris/dentalAnxiety.htm, or from http://homepages.abdn.ac.uk/j.crawford/pages/dept/MDAS_PRs.htm (After downloading the program it can be run by clicking on the program in windows explorer, or, if a shortcut to the program has been created on the user's desktop, by clicking on the shortcut icon).
The program prompts the user to select the patient's gender and age using radio buttons and to enter their MDAS raw score. The output from the program consists of the patient's raw score on the MDAS (as entered by the user), and the point and interval estimates of the percentile rank for the score. These results can be viewed on screen, saved to a file, and/or printed.
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