Participants and data collection
Two online questionnaires were used separately for collecting data from the general public (Additional file 3, Additional file 4) and the FDS (Additional file 1, Additional file 2) in Yichang during a period of time from the 2nd to the 13th of May 2020. The questionnaire for general public (Additional file 3, Additional file 4) only contained questions of personal information and the Beck Anxiety Inventory (BAI) which was used to assess their anxiety state. As for FDS (Additional file 1, Additional file 2), besides these two parts, a short test on their knowledge of COVID-19 were included, and more questions relevant to their work environment and protective measures had been asked. These questionnaires were distributed through social media, such as WeChat and QQ, and were accessible via phone, computer and tablet. Each participant had been informed of this study and their consent had been asked.
In general, 330 questionnaires were distributed to the FDS in Yichang and 280 were received with a completion rate of 84.85%. Meanwhile, 330 questionnaires were distributed to the general public in this area and 285 were received with a completion rate of 86.36%. As for data set provided by FDS, since FDS only referred to dental interns, dental nurses and general dentists, data from 11 volunteers were excluded. Therefore, the sample size of FDS is 269. As for the general public, in order to compare with FDS, only participants of 20–56 were included, leading to a sample size of 258 for the general public group.
Assessment of anxiety state of all participants
The Chinese version of BAI , which is reliable and valid [17, 18], was used in this study to assess the anxiety state of both groups. BAI is a self-rated inventory with 21 items measuring cognitive, emotional and physical aspects of anxiety disorders. Each item was provided with four answers of different scores (1 = not at all, 2 = mildly, 3 = moderately, 4 = severely). The summary of the score of 21 items were applied with the formula Y = int (1.19*x) to calculate the final score for each participant . A final score equals to or was higher than 45 would be counted as having anxiety disorders or otherwise . Hence, the outcome variable is binary.
Potential factors associated with the anxiety state of FDS
Other questions relevant to potential factors were included in the questionnaire for FDS. They were as follow: i) the number of working days per week, ii) the number of working hours per day, iii) the number of working hours between breaks, iv) whether they often performed aerosolization procedures, v) whether they had conflicts with colleagues and/or patients in the last 6 months, vi) whether they had performed treatment on confirmed or suspected cases of COVID-19, vii) whether their skin or wounds were exposed to the blood, saliva, or other body fluids of patients, viii) whether the guideline of PM-3 had been followed in their office.
Another potential factor investigated was the knowledge of COVID-19 among FDS, six multiple choice questions of COVID-19 were used to conduct the assessment. The answers to each question was set according to the Diagnosis and Treatment Protocol for Novel Coronavirus Pneumonia (Trial Version 7) . These questions covered the following aspects regarding COVID-19: i) the common symptoms, ii) the incubation period, iii) the main routes of transmission, iv) the effective measures and chemicals for cleaning and disinfection, v) the discharging criteria for confirmed cases, vi) the susceptibility of people to this disease. There was only one correct answer among four choices for each question. A correct answer was counted as 1 point, otherwise 0 point. The summary score was calculated to assess the knowledge of COVID-19 among FDS.
In this study, the statistical analysis of data was performed via Microsoft Excel version 16.43 (Microsoft Corporation, Redmond, Washington, USA) and SPSS version 26.0 (International Business Machines Corporation, Armonk, New York, USA). Firstly, it was a between group design for the examination of the anxiety state between FDS and the general public. Therefore, after the final scores for participants were calculated, they were classified into two groups as ‘have anxiety disorders’ or ‘doesn’t have anxiety disorders’. Then a Chi-square Test was conducted to determine the difference between FDS and the general public on their anxiety state.
Secondly, the potential factors relating to the anxiety state of the FDS was investigated. Since the relevant questions yielded categorical and numerical data, a Chi-square test and the Cramer’s V were calculated when the association between two categorical variables were studied, and the calculation of Eta squared was applied to study the association between a categorical variable and a numerical variable. The association between each potential factor and the anxiety state of FDS was assessed, so as to the relations between every two potential factors, in order to minimize the influence brought by highly correlated potential factors and to find the potential factors that were moderately or strongly associated with the anxiety state of FDS.
Finally, a binary logistic regression model was developed to examine the relationships between the predictor variables (potential factors) and binary outcome variable (The anxiety state of the FDS).