Permission and translation

The first author obtained permission from Friederike Barthels, corresponding author of DOS, via email to do a validation study of the scale before starting the study. DOS was translated into Turkish by two psychiatrists fluent in both languages. The Turkish version was then back-translated into German and compared to the original scale by linguists who had no prior access to the original scale. Both researchers and linguists approved the Turkish version of the study prior to the research.

Sample and procedure

The study consisted of 130 patients diagnosed with major depressive disorder, 130 patients diagnosed with generalized anxiety disorder, 65 patients diagnosed with obsessive–compulsive disorder according to DSM-5-TR who applied to Mersin City Training and Research Hospital Psychiatry outpatient clinic for treatment between 01.11.2023–01.02.2024, and 120 volunteers who lived in the same environment with the patients, declared that they had not been diagnosed with psychiatric illness before, and were similar to the patient group in terms of sociodemographic variables. Inclusion criteria were being between 18 and 65 years old, being fluent in Turkish, having at least an elementary school education, and not having cognitive impairment or psychotic symptoms. We included 120 healthy individuals without any psychiatric diagnosis who were similar to the patient group in terms of age, gender, and education level to the control group. The control group consisted of hospital staff members’ relatives who expressed willingness to participate in the scientific research. No financial incentives were provided to the participants.

Psychiatric interviews were conducted with all participants according to the DSM-5-TR diagnostic criteria, and diagnoses of MDD, GAD, and OCD were confirmed. To prevent the confusing effect of comorbid mental illnesses, 15 cases with comorbid GAD diagnosis and 3 cases with comorbid OCD diagnosis among MDD cases were excluded from the study. Four cases were excluded from the study because they did not complete the scales. Among GAD-diagnosed cases, 4 cases with comorbid MDD diagnosis, 5 cases with comorbid panic disorder diagnosis, and 4 cases who did not complete the scales were excluded from the study. Among OCD-diagnosed cases, 5 cases with comorbid MDD diagnosis and 4 cases who did not complete the scales were excluded from the study. From the control group, 5 participants who did not complete the scales, 4 participants diagnosed with somatic symptom disorder, 4 participants diagnosed with alcohol use disorder, and 3 participants diagnosed with bipolar disorder were excluded. We continued the study with 117 patients diagnosed with GAD, 108 patients diagnosed with MDD, 56 patients diagnosed with OCD, and 104 healthy volunteers. Taking into account the potentially confounding effects of different types of medications, we excluded patients using medications other than selective serotonin reuptake inhibitors (SSRIs) or serotonin-norepinephrine reuptake inhibitors (SNRIs) monotherapy. All patients had been receiving SSRI-SNRI monotherapy for at least 3 months. To assess test–retest reliability, we administered DOS to 70 participants who completed the first test and were reachable at two-week interval. The study was approved by the Toros University Scientific Research and Publication Ethics Committee with decision number 115 dated 27.10.2023. Necessary permissions were obtained from Mersin City Training and Research Hospital to recruit patients. All participants completed the informed consent form. The study was conducted in accordance with the Helsinki Declaration.

Sample size

In validity and reliability studies, it is recommended to have at least 5 to 10 times the number of items in the scale as participants [30]. Power analysis for the study was conducted using G Power 3.1 software. It was calculated that a total of 280 participants across 4 groups would be required for an effect size of 0.25, a margin of error of 0.05, and a power of 0.95, and with a total of 385 participants, it was believed that this study had sufficient power [31].

MeasuresSociodemographic and clinical data form

In this form, sociodemographic data such as age, sex at birth, marital status, educational status and place of residence are questioned.

Hamilton depression rating scale (HAM-D)

It is a clinician-administered likert-type scale consisting of 17 questions, measuring the severity of depressive symptoms [32]. Higher scores indicate increased depressive symptoms. In the Turkish validity and reliability study, the Cronbach’s alpha value was found to be 0.75 [33]. In our study, Cronbach’s alpha coefficient was calculated to be 0.82.

Hamilton anxiety rating scale (HAM-A)

It is a clinician-administered likert-type scale consisting of 14 items used to measure the severity of anxiety [34]. The scale has 5 items questioning psychic symptoms and 9 items questioning somatic symptoms. The total score of these two subscales yields the scale score. In the Turkish validity and reliability study, the correlation coefficients of the items were found to be 0.72 individually, and 0.94 as total [35]. In our study, Cronbach’s alpha coefficient was calculated to be 0.90.

The Yale–Brown obsessive–compulsive scale (Y-BOCS) and symptom checklist

It is a clinician-rated scale developed to measure the type and severity of obsessive–compulsive symptoms [36]. The YBOCS consists of a total of 19 items, with scores evaluated for the first 10 items (excluding items 1b and 6b). Items 1–5 assess the severity of obsessions, while items 6–10 assess the severity of compulsions. As scores increase, the severity of the disorder also increases. In the Turkish validity and reliability study, the Cronbach’s alpha value was calculated to be 0.81 [37]. In our study, Cronbach’s alpha coefficient was calculated to be 0.90.

The eating attitude test (EAT-40)

It was developed to screen for eating disorders, primarily anorexia nervosa (AN) [38]. It is a self-report scale consisting of 40 questions rated on a 6-point Likert-type scale. The total score of the scale is obtained by summing the scores obtained from each item. Participants scoring thirty or higher are considered to be in the high-risk group for eating disorders, primarily AN [38]. In the Turkish validity and reliability study of the scale, the Cronbach’s alpha value was found to be 0.70 [39]. In our study, Cronbach’s alpha coefficient was calculated to be 0.80.

The orthorexia nervosa inventory (ONI)

It is a four-point Likert-type self-report scale developed to assess emotional, behavioral, physical and psychosocial impairments related to pathological focus on healthy eating [40]. The three-factor scale consists of 24 items, assessing emotions with 5 items, behaviors and preoccupation with healthy eating with 9 items, and physical and psychosocial disturbances with 10 items. The lowest score that can be obtained from the scale is 24, and the highest score is 96. The cutoff score is determined as 72 [40]. As scores increase, orthorexic symptoms also increase. In the validity and reliability study of the Turkish version, Cronbach’s alpha coefficient was calculated to be 0.91 [41]. In our study, Cronbach’s alpha coefficient was calculated to be 0.92.

The Düsseldorf orthorexia scale (DOS)

It is a four-point self-report Likert-type scale created to assess orthorexic symptoms, consisting of 10 items [21]. Scores range from 10 to 40. Items are marked between "definitely applies to me" (4 points) and "definitely does not apply to me" (1 point). As scores increase, orthorexic symptoms also increase. In studies, it has been reported that scores between 25 and 29 indicate a high risk of ON, while scores of 30 or above indicate the presence of ON [21, 42]. The Cronbach’s alpha value of the scale is 0.84, and the test–retest reliability ranges from 0.67 to 0.79 [21].

Statistical analysis

Descriptive statistics were presented in tabular form, indicating mean ± standard deviation or median, minimum and maximum for continuous variables depending on the distribution to summarize the data obtained from the study. Categorical variables were summarized as numbers and percentages. The normality of numerical variables was assessed using the Shapiro–Wilk, Kolmogorov–Smirnov, and Anderson–Darling tests.

To determine differences in categorical variables between diagnostic groups, the Pearson Chi-Square test was used for cases with 5 or more observations. For group comparisons of numerical variables, the One-Way ANOVA test was applied if the data showed normal distribution, and the Kruskal–Wallis H test was used if they did not. For multiple comparisons, the Games-Howell or Tukey test was used for parametric tests, and the Dwass-Steel-Critchlow-Fligner test was used for non-parametric tests.

To determine the structural properties of the DOS, Exploratory Factor Analysis (EFA) was conducted. In EFA, the principal axis factoring method was used to extract factors. Internal consistency analysis was performed to evaluate the reliability of the DOS. In this analysis, Cronbach’s alpha coefficient and each Cronbach’s alpha value obtained when each item was extracted were examined. Test–retest reliability of the scale was calculated using the intraclass correlation coefficient.

After conducting EFA to validate the structure defined for the DOS, Confirmatory Factor Analysis (CFA) was performed to validate this structure. Since the Mardia test indicated that multivariate normal distribution was not met, robust maximum likelihood estimation based on the covariance matrix was used in CFA. Comparative Fit Index (CFI), Normed Fit Index (NFI), Goodness of Fit Index (GFI), and Root Mean Square Error of Approximation (RMSEA) were considered to evaluate the goodness of fit of the model.

To assess the validity of the DOS, its relationships with the ONI, EAT, HAM-D, and HAM-A scales were examined using correlation analysis. Statistical analyses were conducted using Jamovi (Version 2.3.28), JASP (Version 0.18.3), and LISREL (version 8.50) softwares. A significance level of 0.05 (p-value) was used for all analyses.