Table 2 Description of primary outcome scales

Self-efficacy

Modified Grossman Self-efficacy for Diabetes Scale[36, 37]

The scale contains 25 items that measure the intensity of self-efficacy for activities of the diabetes regimen. Subjects are asked to describe how much they believe they could or could not do what was stated. The responses on this 6-point scale range from “very sure I can’t” to “very sure I can” do what was stated in each item. Higher scores indicate greater confidence in one’s ability to perform the designated treatment activities. The following statements are examples of the self-efficacy items: “Figure meals and snacks at home” and “Keep track of blood sugar levels”. The modified self-efficacy scale has a moderate to high reliability (Cronbach’s alpha = 0.51 to 0.86).

Self-care behavior

Summary of Diabetes Self-Care Activities Measure – Revised[38, 39]

Items selected from this self-report instrument assess participants’ frequency (over the past 7 days) of engaging in diabetes self-care behaviors, including following a healthy diet, spacing out carbohydrates evenly across the day, physical activity, self-monitoring of blood glucose testing, foot care, and medication and/or insulin taking. For each diabetes self-care behavior, participants are asked to respond using the following prompt: “On how many of the last 7 days…” Responses, which are based on a 7-day week, range from 0 days to 7 days. Greater number of days indicated better self-management. Reliability and validity for this instrument have been found to be adequate, with a test-retest correlation of 0.40 and internal consistency of 0.47.

Diabetes-specific quality of life

Diabetes Distress Scale[40]

The DDS is a 17 item instrument that assesses emotional distress and functioning specific to living with diabetes. Responses are scored on a 6-point Likert-type scale from 1 = “no problem” to 6 = “serious problem”. Scores can range from 17–102 with higher scores indicating poorer diabetes-related quality of life and lower scores indicating better diabetes-related quality of life. The DDS has been found to have high internal reliability with a Cronbach’s alpha of 0.93, good convergent validity with the Center for Epidemiological Studies Depression Scale (CESD) (r = 0.56) and self-care behaviours including lower adherence to eating recommendations (r = 0.30, p < 0.001) and lower levels of physical activity (r = 0.13, p < 0.01)[40]. In addition, diabetes distress has been demonstrated to be associated with HbA1c (r = 0.17-0.31, P = .00-.001), diet (r = −0.38, P = .00), physical activity (r = −0.13, P = .01) and medication adherence (r = −0.16, P = .00)[41, 42].