Study design, setting, and participants
A questionnaire-based, cross-sectional study was conducted between November 2013 and March 2014. Consecutive sampling was used to recruit all outpatients with type 2 diabetes who visited an endocrinologist on a specific date and at four locations in Japan, specifically, two university hospitals, one non-university-affiliated hospital, and one non-university-affiliated clinic. Patients were recruited through their physicians. After obtaining permission from the physicians, the patients received an explanation of the study's purpose by the research staff, after which written informed consents were collected. Inclusion criteria were as follows: presence of type 2 diabetes; aged 20–74 years; ability to read and speak Japanese; no diagnosis of dementia and psychosis; and no urgent medical procedures or examinations needed. Patients completed a questionnaire, taking approximately 15–20 min.
This study was approved in advance by the Research Ethics Committee of the University of Tokyo Graduate School of Medicine and Faculty of Medicine, and by each participating facility.
Variables
Participants’ sociodemographics included sex, age, education (in years), and marital status. A patient's level of education was collected as categorical data (have not graduated high school, have graduated high school, technical/junior college, or earned bachelor's degree or higher) and then converted into years of schooling. Marital status was collected as categorical data (married, unmarried, divorced, or bereaved) and then summarized into two categories (married or unmarried/divorced/bereaved).
Participants’ clinical information, such as body mass index (BMI), time since diagnosis (in months), injection therapy, diabetes-related complications, and hemoglobin A1c level (HbA1c), was also collected. Injection therapy was collected as categorical data (oral hypoglycemic agents, insulin injections, insulin injections and oral hypoglycemic agents, other injectable medications (other than insulin), or lifestyle). This information was then summarized into two categories (injection use or non-use). The number of diabetes-related complications was calculated as the simple sum of six complications, referring to the Diabetes Complications Index (DCI).30 The score ranged from 0 to 6. HbA1c level was completed based on a copy of the laboratory results received that day.
Self-stigma
The Self-Stigma Scale was used to assess the level of self-stigma.31 The reliability and validity of the scale's Japanese version (SSS-J) were reported previously.32 The scale comprises 39 assessment items, allowing four responses on a Likert scale: strongly disagree, disagree, agree, and strongly agree, scored 0, 1, 2, and 3, respectively. The total possible scores ranged from 0 to 117, and the score was treated as continuous. A higher score represents a higher level of self-stigma. In this study, the scale had an internal consistency of 0.96.
Patient activation
The Patient Activation Measure (PAM-13) was used to assess patient self-engagement in the treatment.33–35 The PAM-13 can be used as a suitable approximation for self-care behaviors since behaviors are clearly associated with patients’ activation levels. Patient activation is a concept that includes a comprehensive approach to a number of elements related to activation, including the knowledge, skills, confidence, and behaviors that a patient needs to manage their illness. Therefore, in this study, the PAM-13 was used to assess patients’ self-care behaviors.
The PAM-13 is a clinically used, highly reliable and valid scale containing 13 questions, scored using a Likert scale (strongly disagree, disagree, agree, strongly agree, and not applicable). A score of 1, 2, 3, 4, or missing was chosen, with a possible total score of 13 to 52. These scores were then converted into an interval scale (0–100). A high score corresponds with a positive attitude toward the necessary behavioral changes during the course of treatment. The Japanese version of the PAM-13 for mental health was used without including the words ‘mental health’ as stipulated by the scale's developer. In this study, the scale had an internal consistency of 0.85.
Self-efficacy
The General Self-efficacy Scale was applied to assess individual strengths in the general self-efficacy across a variety of everyday life settings.36 It is reliable, valid, and commonly used to measure self-efficacy in Japan; it is a 16-item scale and uses dichotomous (yes/no) questions. The total possible scores have a range of 0–16, and the score was treated as continuous. A higher score represents a higher level of self-efficacy. In this study, the scale had an internal consistency of 0.84.
Depression symptoms
The nine-item depression module of the Patient Health Questionnaire (PHQ-9) was used to assess patients’ depression symptoms over the 2 weeks prior to filling out the questionnaire.37 ,38 The PHQ-9 is a reliable and valid measure of depression severity for clinical use. Each item is scored on the DSM-IV (Diagnostic and Statistical Manual of Mental Disorders-IV) criteria from 0 (not at all) to 3 (nearly every day). The total possible scores have a range of 0–36, and the score was treated as continuous. In this study, the scale had an internal consistency of 0.86.
Statistical methods
Descriptive statistics were calculated using means and SDs, or numbers and percentages, based on the nature of the variables. Dummy variables were created for categorical variables (ie, sex, marital status, and injection therapy). Patient activation was considered a dependent variable, whereas self-stigma, self-efficacy, and depression symptoms were considered independent variables. Each independent variable's relationship to the dependent variable was evaluated using scatterplots and Pearson's correlation coefficient. Before analyses, we tested the model's assumptions: linearity of the relationship among the dependent and independent variables, the homogeneity of variance (relation between the standardized and studentized residuals), the normality of residuals (histogram and normal QQ plot of the residuals), and multicollinearity (variance inflation factor (VIF) and tolerance test).
Multiple linear regression models were analyzed to assess the independent effect of self-stigma on patient activation for self-care behaviors, and two models were constructed. Based on literature reviews, we adjusted for covariates from the possible influence of sociodemographic and clinical variables including sex, age, BMI, diabetes duration, injection therapy, number of diabetes-related complications, HbA1c, education, and marital status. These sociodemographic and clinical variables, except sex, injection therapy, and marital status, were included in the models as continuous variables. A direct method was used for the multiple linear regression analyses.
To examine the models’ predictive capacity, analysis of variance was used to test the significance of the overall regression equation by calculating the F value. The adjusted coefficients of determination were calculated to evaluate the explanatory capacity of patient activation. Regression coefficients and standardized partial regression coefficients were also calculated to quantify the degree of association between the dependent and independent variables. All analyses were performed using SPSS V.23.0 (SPSS Japan Inc, Tokyo, Japan).