This study aimed to psychometrically assess the D-Lit questionnaire. Based on the results of EFA, the questionnaire had 5 subscales with specific values greater than 1, which was able to predict 56.30% variance. In the CFA stage, these 5 factors were examined and one question was removed and finally, the questionnaire with 5 factors and 21 questions was approved. The reliability of the questionnaire was assessed using Cronbach's alpha and Omega-McDonald's coefficient, which were 0.890 and 0.891, respectively, for all questions.
In Griffiths et al. study, the validity and reliability of the questionnaire were examined and Cronbach's alpha and 3 month test-retest reliability were reported 0.70 and 0.71, respectively [24]. The Griffiths study showed that this questionnaire is a suitable tool to assess the depression literacy status. Also, results showed that depressive literacy may be useful in reducing social stigma in people with depression [24]. In a study conducted by Wang with the aim of psychometric evaluation of the D-Lit questionnaire on Chinese people, the results showed that Cronbach's alpha and content validity were 0.885 and 0.989, respectively, and the Chinese version of this questionnaire had acceptable validity and reliability for assessing the knowledge of people about depression [44]. In a study conducted by Arafat to psychometrically evaluate the Bangla version of the D-Lit questionnaire, the Cronbach's alpha was 0.77. After validity and reliability, according to the expert’s opinion, 3 questions were removed due to cultural equivalence and one question was added to the questionnaire and finally, the 20-question version of the questionnaire with one factor was confirmed [27]. In a study aimed at psychometric evaluation of the Arabic version of the D-Lit questionnaire, Cronbach's alpha coefficient, split-half test, test-retest, and Spearman's correlation were 0.78, 0.71, 0.92, and 0.91, respectively. None of the questionnaire questions were removed and the 22-item version of the questionnaire was approved by one factor [25].
In the Ibrahim study conducted in the Malaysian population, 5 questions were removed from the D-Lit questionnaire and Cronbach's alpha of the questions was 0.6 [45]. The results of the Oliffe study in the Canadian male population showed that Cronbach's alpha of D-Lit questionnaire was 0.74 [46]. A study of the Korean American population by Bernstein showed that the Cronbach's alpha of the D-Lit questionnaire was 0.81 [47]. In the Ram study on healthcare profession students, the results showed that Cronbach's alpha of the questionnaire was 0.74 [48]. The results of the Kiropoulos study in Australia showed that Cronbach's alpha levels of D-Lit questionnaire in the Greek and Italian populations living in Australia were 0.88 and 0.99, respectively [49]. In a study conducted by Bonabi in the United States, the Cronbach's alpha of the D-Lit questionnaire was 0.89 [50].
A study conducted by Jeong on Korean pregnant women showed that the content validity of the parental D-Lit scale was 0.875. During the validity and reliability, 4 questions were removed from the questionnaire. Results of EFA showed that the questionnaire has 3 factors of misperceptions about depression and its treatment, knowledge about the treatment of depression, and knowledge about depression. The results of CFA showed that the RMSEA, CFI and χ2/df indices were 0.056, 0.813, and 1.44, respectively, which confirmed these three factors. Finally, the questionnaire was approved with 18 questions and three factors [26].
In this study, the first factor was “knowledge of the psychological symptoms”, which was confirmed by 5 questions, standard regression coefficient 0.640 to 0.729, Cronbach's alpha coefficient 0.837, and omega McDonald coefficient 0.838. knowledge about the psychological symptoms of depression is effective in seeking mental health services [51]. The results of a study showed that people with higher levels of depression had less knowledge about recognizing depression and seeking professional help-seeking than people with low levels of depression [16]. The results of a study showed that most people had little knowledge about depression and had poor diagnostic ability about depression [52].
The second factor in this study was the “knowledge about the effectiveness of available treatment methods”, which were confirmed by 4 questions, the standard regression coefficient 0.470 to 0.797, Cronbach's alpha coefficient of 0.767, and the omega McDonald coefficient of 0.779. Most people with mental disorders do not use mental health services because they are unaware of the available treatments [53]. Also, the most important reason for patients with mental disorders to delay receiving treatment is the lack of knowledge about available effective treatments. Therefore, having sufficient knowledge about effective treatment methods for mental disorders seems to be necessary [54]. Treatment of depression in the early stages reduces the symptoms of the disease and prevents of severe depression [55].
In the present study, the third factor was “knowledge about cognitive-behavioral symptoms” which was confirmed by 6 questions, standard regression coefficient 0.536 to 0.610, Cronbach's alpha coefficient 0.739, and omega McDonald coefficient 0.740. Another aspect of depression is cognitive-behavioral problems and major cognitive symptoms of depression include difficulty concentrating and decision problems [56]. Having these symptoms can cause the person to not be able to diagnose the problem and not pay attention to the available information. Therefore, knowledge about the cognitive-behavioral symptoms of depression is essential for the early diagnosis of diseases [57, 58].
The fourth factor was “knowledge about taking medications and their side effects”, which was confirmed by 4 questions, standard regression coefficient 0.495 to 0.693, Cronbach's alpha coefficient 0.723, and Omega McDonald coefficient 0.728. Opinions differ on the effectiveness of antidepressants in relieving depressive symptoms. Antidepressants, like many other treatments, may help in some cases and not be useful in others. These medications of depression can also have side effects similar to other medications. People with depression should be sufficiently knowledge of this and receive the necessary information from their physician about the pros and cons of antidepressants [59].
In this study, the fifth factor was “knowledge of the severity of the disease”, which was confirmed by 2 questions, standard regression coefficient of 0.533 and 0.639, Cronbach's alpha coefficient of 0.522, and Omega-McDonald coefficient of 0.522. Another important factor is having the right knowledge about the disease. A study finding showed that many public people are not able to recognize specific disorders or different types of mental disorders [15]. The results of a study in China showed that people who more learned about mental disease had more knowledge about the mental health [60]. A randomized controlled trial showed that the intervention of web-based D-Lit had a significant decrease in the stigmatizing attitudes of people who experienced depression with severe symptoms [61]. Therefore, having accurate and reliable information about the disease is essential and allows the person to refer to the systems providing mental health services without fear of treatments and use the available treatments [62–64]. One of the strengths of this study was that the study was conducted with a high sample size. Also, this study was conducted on the general population and this questionnaire can be used for different target groups. One of the limitations of this study was that the reliability of the study was not performed using the test-retest method. Due to the COVID-19 pandemic, it was not possible to perform the test-test. Another limitation of this study was that the information was completed using a questionnaire and self-report and may have some errors. In this study, people with a clear diagnosis of mental health problems were not included in the study because people with mental health disorders due to referral and follow-up treatment may have high levels of depression literacy.