In total, 107 residents (response rate: 28.2%) at 18 teaching hospitals in 11 prefectures responded to the questionnaire. After excluding invalid responses, such as choosing the same options, data from 97 residents (41 residents in hospitals with 500 beds or more, 36 in hospitals with 300–499 beds, and 20 in hospitals with 299 beds or less; 62 in the third month of their residency program and 35 in the fifteenth) were used for the analysis.
Table 1 shows the respondents’ demographic data and working environments. The residents’ average ages in the third and fifteenth months were 26.7 and 27.6 years, respectively, average frequency of night duty was 3.6 times per month, and average number of working hours per day was 11.5, which is equivalent to 63.3 hours per week.
Confirmation of scales
Exploratory factor analysis with promax rotation of the Japanese versions of the MBI and SOC scale using data from the 97 respondents indicated a six-factor structure (Table 2). Factors 1, 2, and 4 had items identical to the MBI-PE, MBI-EX, and MBI-CY detected in the original English version. The three-factor structure of the original version of the SOC scale did not detect these in the present analysis, and two items on the SOC scale were classified into factor 1 (MBI-PE); one item had a loading of over 0.4 for factor 4 (MBI-CY) and factor 6. These three items were excluded, and thus, 10 items of the SOC scale (SOC10) were used for the analysis.
Cronbach’s a coefficients for the MBI-EX, MBI-CY, and MBI-PE were 0.91, 0.88, and 0.89, respectively. Cronbach’s a coefficient for the SOC10 was 0.81.
MBI-GS subscale scores, burnout frequency, and influential factors
As shown in Table 3, the residents’ mean MBI-EX, -CY, and -PE scores were 15.2, 7.7, and 16.4, respectively.
Among 97 respondents, 48 (49.5%) were judged as having burnout (Table 4). The frequencies of burnout in the third and fifteenth months were 53.2% and 42.9%, respectively, with no significant difference. The frequencies of burnout among men and women were 49.2% and 50.0%, respectively; gender was not a significant factor.
Logistic regression analysis of burnout using gender, frequency of night duty, working hours, age, work controllability, and the SOC10 as independent variables indicated that working hours (odds ratio [OR]: 1.315, 95% confidence interval [CI]: 1.057–1.636, p=0.014) and the SOC10 (OR: 0.928, 95% CI: 0.882–0.976, p=0.004) were significant factors for having burnout. The SOC10 (OR: 0.918, 95% CI: 0.854–0.986, p=0.018) and frequency of night duty (OR: 0.615, 95% CI: 0.388–0.974, p=0.038) were significant variables for burnout for respondents in the third and fifteenth months of the residency program, respectively.
MBI subscale scores at different training phases
At the third month, 32 (51.6%, 97.0% of burned out residents), 16 (25.8%, 48.5% of burned out residents), and 47 (75.8%) residents were judged as having abnormally high scores on the MBI-EX and MBI-CY, and low scores on the MBI-PE, respectively (Table 5).
At the fifteenth month, 12 (34.3%, 80.0% of burned out residents), 9 (25.7%, 60.0% of burned out residents), and 30 (85.7%) residents were judged as having abnormally high scores on the MBI-EX and MBI-CY, and low scores on the MBI-PE, respectively.
Chi-square test and t-test indicated that the frequency of abnormal subscale scores and average subscale scores between the third and fifteenth months were not significantly different.
MBI subscale scores, SOC10 score, and working hours
The average SOC10 score of the 97 residents was 45.0 (standard deviation 10.1) (Table 3). Thirty residents (62.5%) in the low SOC group (SOC10≤45, n=48) and 18 (36.7%) in the high SOC group (SOC10>45, n=49) were judged as having burnout (Table 4).
The MBI subscale scores in the low and high SOC groups in the third and fifteenth months are shown in Table 6. MBI-EX, -CY, and -PE scores between the low and high SOC groups at the third month, and MBI-CY, and -PE scores between the low and high SOC groups at the fifteenth month were significantly different by t-test (p<0.05).
In the low SOC group, the Pearson correlation coefficients between working hours and all three MBI subscale scores were significant in the third month (MBI-EX: r=0.47, p=0.007; MBI-CY: r=0.39, p=0.029; MBI-PE: r=–0.44, p=0.012), but not in the fifteenth. In the high SOC group, working hours correlated with only MBI-PE in the third month (r=0.36, p=0.049) (Table 6).
To analyze the relationship between working hours, SOC scores, and MBI subscale scores, the respondents were divided into four groups: ≤9 hours (19 residents), >9 to 11 hours (29 residents), >11 to 13 hours (32 residents), and >13 hours (17 residents) per day.
As shown in Figure 1, two-way analysis of variance with working hours and SOC scores as factors of the MBI-EX score revealed that working hours and SOC scores were significant variables in the third and fifteenth months, respectively. Regarding the MBI-CY and MBI-PE scores, SOC was a significant variable in both the third and fifteenth months. The MBI-PE score in the high SOC group was higher (more professional efficacy) in longer working hour groups, whereas the MBI-PE score of the low SOC group was lower (less professional efficacy) in longer working hour groups.