The overall aim of this study was to understand the determinants of diabetes and the variations in diabetes outcomes and care for people with SMI. We also aim to identify health-care interventions that are associated with better outcomes, which can be tested further. The study feeds into a wider research programme to improve diabetes outcomes for people with SMI.
Research questions
Our key research questions were as follows:
- What are the sociodemographic and illness-related risk factors associated with –
- diabetes developing in people with SMI?
- variations in diabetes and mental health outcomes in people with SMI and diabetes?
- How do physical and mental health outcomes differ between people with SMI and diabetes and people with –
- SMI without diabetes?
- diabetes but no SMI?
- What factors are associated with access to and receipt of diabetes health care for people with SMI, and how are diabetes health-care interventions experienced by people with SMI?
- How, and at what cost, is diabetes monitored and managed in people with SMI, compared with people without SMI?
- What health-care interventions (e.g. medication, referrals and care pathways) are associated with better diabetes outcomes for people with SMI and diabetes?
These questions are addressed in two studies, with seven objectives (see Study objectives). The quantitative study (see Chapter 5) addresses objectives 1–4, 6 and 7; the qualitative study addresses objective 5 and also contributes to objectives 2 and 7 (see Chapter 6).
Study objectives
- In people with SMI: to identify which sociodemographic, illness, family history and lifestyle factors are associated with the development of diabetes (see Chapter 5, Objective 1: factors associated with the development of diabetes in people with severe mental illness).
- In people with SMI and diabetes: to identify which sociodemographic, illness, family history and lifestyle factors are associated with variations in diabetes and mental health outcomes (see Chapter 5, Objective 2: factors associated with variation in diabetes and mental health outcomes in people with severe mental illness and diabetes).
- In people with SMI: to compare the health-care interventions and physical and mental health outcomes of people with diabetes with those of people without diabetes (see Chapter 5, Objective 3: comparing health-care interventions and health outcomes in people with severe mental illness with diabetes with those in people with severe mental illness without diabetes).
- In people with diabetes: to compare the health-care interventions and physical and mental health outcomes of people with SMI with those of people without SMI (see Chapter 5, Objective 4: comparing the health outcomes of people with diabetes and severe mental illness with the health outcomes of people with diabetes without severe mental illness).
- To understand the factors that are associated with access to, and receipt of, diabetes care for people with SMI, and to explore the experience of diabetes health care by people with SMI (see Chapter 6).
- To compare diabetes care provision for people with and people without SMI, and to estimate costs for these (see Chapter 5, Objective 6: comparing diabetes care provision and estimating health-care costs for people with and people without severe mental illness).
- To identify which health-care interventions (e.g. medication, referrals and care pathways) may be associated with better diabetes outcomes for people with SMI and diabetes (see Chapter 5, Objective 7: identifying health-care interventions associated with better outcomes for people with diabetes and severe mental illness).
Deviations from the study protocol
The protocols for the overall study and for the quantitative study (study reference: 17_161R) have been published and are publicly available.103,104
There were some changes to the study protocol for the quantitative analyses.
First, we planned to stratify all analyses by ethnicity. However, the small numbers in minority ethnic categories precluded doing this for some analyses.
Second, for objective 2 (see Chapter 5, Objective 2: factors associated with variation in diabetes and mental health outcomes in people with severe mental illness and diabetes), the methods were changed from repeated measures to patient-level analysis, as the former did not add value.
Third, for objective 7 (see Chapter 5, Objective 7: identifying health-care interventions associated with better outcomes for people with diabetes and severe mental illness), following discussions with clinical experts at a research team workshop, we had planned to look at several physical health checks including blood pressure, cholesterol, HbA1c, body mass index (BMI), retinopathy screening, diabetes education and influenza vaccination. However, we were unable to explore in detail all health-care interventions that we originally planned as a result of inconsistencies in the recording of relevant activities in patient records. We therefore prioritised investigating the most common physical health checks, including blood pressure, cholesterol, HbA1c level and BMI, for which recording was more complete.
Fourth, we identified that a significant proportion of the study population had diabetes diagnosed before the onset of SMI. Therefore, we needed to explore any potential order of diagnosis effects; these investigations were added to the planned analyses.
Fifth, for the final integration of study findings, we did not develop a logic model as proposed in the protocol, because of the tentative findings about how diabetes care provision may be associated with outcomes in people with SMI and diabetes.
There were no deviations from the study protocol for the scoping of the literature or the qualitative study.