A biopsychosocial model of diabetes self-management: Mediators and moderators by Karen Glaister This thesis is presented for the degree of Doctor of Philosophy at Murdoch University, 2010 i
Declaration I declare that this thesis is my own account of my research and contains as its main content, work which has not been previously submitted, in whole or part, for a degree at any tertiary institution. Karen Glaister 13 November, 2010 i
Perhaps our most important quality as humans is our capability to self-regulate. It has provided us with an adaptive edge that enabled our ancestors to survive and even flourish when changing conditions led other species to extinction (Zimmerman, 2000, p.13). ii
Abstract Diabetes mellitus (diabetes), an endocrine disorder, is in epidemic proportions globally, threatening the well being of people affected and challenging health care systems. In the main, diabetes warrants adjustments to lifestyle and therapeutic interventions simply to self-manage the condition. Research in self-management of diabetes has targeted sociocognitive theory and espoused self-efficacy as the main driver of self-management. More recently, self-regulatory theory has focused on illness representations and argued they are the force underpinning goal directed. Research to-date has tended to adopt one or other of the prevailing theoretical models to the exclusion of key concepts in other explanatory health behaviour models. Studies are lacking in demonstrating a comprehensive exploration of the interrelationships between self-regulatory skills inherent in self-management, illness representations and self-efficacy with other potential health behaviour determinants. In this thesis, it was postulated that an integrated biopsychosocial model of self-management was warranted to account for the complexities of human understanding and interactions within a naturalistic setting. The purpose of this dissertation was to develop and substantiate a conceptual model of diabetes self-management integrating key concepts from health behaviour theories within a structure of four broad determinants of health behaviour, which were: personal traits, diabetes traits, socio-environmental factors and health contextual factors. Specifically, determinants associated with diabetes self-management and the predictors for its success for those with type 1 and type 2 diabetes was sought. In order to substantiate the proposed integrated model a cross-sectional design, using quantitative survey methodology, was undertaken. Structural equation modelling allowed interrelationships in the integrated model to be explored simultaneously and advanced model testing thus far in the field. The study involved males (n = 504) and females (n = 519), aged over 18 years (M = 63.90, SD = 13.89) who had a diagnosis of either type 1 or type 2 diabetes and who resided in Western Australia. Model testing substantiated the integrated biopsychosocial model proposed and was relatively parsimonious, making the application of the findings to a clinical setting possible. Key predictors for both types of diabetes were: self-efficacy, diabetes distress, iii
diabetes traits, self-determination support by health care professionals and to some extent age of the person with diabetes. In addition, locus of control by doctors was important for type 2 diabetes and marital status and socio-economic status for type 1 diabetes. The presence of emotional distress had a negative effect on interrelated factors, emphasising the criticality of its assessment and management by health professionals if self-management is to be achieved. Illness representations had low or minimal predictive power, refuting claims that it is responsible for the initiation of goal directed. The integrated model, a first of its kind in the Australian context, contributes to existing knowledge in diabetes self-management through its attention to contextualising the selfregulatory individual within their personal, social and health environment. In particular it makes explicit the distinguishing integrated predictors for type 1 and type 2 diabetes previously unknown in the adult population. Through the understanding of predictors, the health sector is better placed to target predictors in supporting self-management. iv
Dedication To my dad, for sharing enough of his mathematical intellect for me to survive structural equation modelling, which presented formidable challenges at every turn! v
Acknowledgements This work is marked by the contributions of so many people; it would be remiss of me not to make mention of them: Firstly, to those who assisted directly with this work. My sincere thanks extend to my supervisors, Professor Simone Volet and Associate Professor Irene Styles, for sharing their academic excellence with me. Their direction and guidance was invaluable and their commitment inspirational. To Dr Everada Cunningham, for coming to my rescue; I am indebted to Arda for her willingness to share her wisdom in applying SEM procedures. Secondly to my family, who remain incredulous at the commitment and time taken to complete this study. In particular, to John, my husband, and Jodie and Libby, my girls, who sustain me in every way with their love and support. Thanks for the many evening where we sat folding and stuffing envelopes with 10,000 surveys; the future holds promise for more engaging activities! Thirdly, to friends and colleagues who have made me laugh, commiserated with me during the dark periods and generally kept me sane. Acknowledgement must also be given to support received from DiabetesWA, who assisted in every way they could with the dissemination of the survey. To the pharmacists across the state, diabetes support group leaders, staff at the NDSS distribution centre and to people with diabetes for completing the long survey. I am indebted to you. Special mention is made to financial support received as the 2007 recipient of the Helen Bailey Scholarship, sponsored by the Department of Health, Western Australia. The money assisted in covering the costs of surveys and their distribution and time release from work at critical periods in the early stages of data collection. vi
Contents DECLARATION ABSTRACT DEDICATION ACKNOWLEDGEMENTS TABLE OF CONTENTS i iii v vi vii PART 1: EMPIRICAL EVIDENCE FOR THE STUDY 1 Chapter 1 INTRODUCTION: DIABETES MELLITUS A CHRONIC 2 CONDITION Chapter overview 3 Background to the study - Conceptualising diabetes as a chronic 5 condition The nature of chronic conditions 5 Diabetes mellitus (diabetes) 9 Health care response 12 Theoretical underpinnings of the study: 14 Diabetes self-management 14 Self-regulation in health and illness 15 Illness representations 17 Purpose of the study 18 Aims and objectives of the study 19 Significance of the study 20 Structure of the thesis 21 Chapter 2 THE SELF IN DIABETES CARE 22 Chapter overview 23 Self-management 24 Self-management expectancies 27 Factors mediating and moderating self-management 31 Self-management in health 42 Self-regulation 44 Self-regulation defined 45 Characteristics of self-regulation 47 Factors mediating and moderating self-regulation 51 Assessing self-regulation 57 Chapter summary 59 Chapter 3 ILLNESS REPRESENTATIONS 61 Chapter overview 62 The construct of illness representations 62 The dimensions of illness representations 63 Illness representations and health outcomes 69 Factors mediating and moderating illness representations 71 Personal attributes 71 vii
Disease traits 73 Socio-environmental context 74 Health context 77 Chapter summary 78 PART 2: CONCEPTUAL MODEL AND STUDY DESIGN 80 Chapter 4 MODELLING SELF-MANAGEMENT 81 Chapter overview 82 Self-management models in health 83 Health behaviour models 83 Self-regulation models 88 The commonsense model of self-regulation 93 Representation of the health threat 94 Coping and Appraisal 95 The conceptual framework for the study 96 Chapter summary 103 Chapter 5 RESEARCH METHODOLOGY 104 Chapter overview 105 Study setting 105 Study design 106 Study participants 107 Study survey 110 Instrument selection 110 Data collection procedure 112 Validating the survey 112 Recruitment 114 Data analysis 116 Instrument validity and reliability 116 Summary statistics 117 Univariate and multivariate analysis 121 Structural equation modelling 122 Ethical considerations 128 Chapter summary 129 PART 3: RESEARCH RESULTS 130 Chapter 6 RESULTS 1: STUDY VARIABLES 131 Chapter overview 132 Univariate analysis independent variables: 132 Personal attributes 132 Disease traits 150 Socio-environment context 155 Health context 162 Univariate analysis dependent variables: 170 Illness representations 170 Self-regulation 178 Self-management 183 Chapter summary 186 viii
Chapter 7 RESULTS 2: RESEARCH OBJECTIVES 1 AND 2 190 Chapter overview 191 Research objective 1 191 Personal attributes and diabetes self-management 192 Disease traits and diabetes self-management 196 Socio-environment and diabetes self-management 200 Health context and diabetes self-management 206 Research objective 2 212 Self-efficacy and illness representations, self-regulation and self- 213 management Illness representations and, self-regulation and self-management 215 Self-regulation and self-management 216 Chapter summary 219 Chapter 8 RESULTS 3: STRUCTURAL EQUATION MODELLING 220 Chapter overview 221 Pre-analysis data preparation 222 Missing data 222 Data distribution 223 Sample size 225 Model specification 226 Study one type 2 diabetes 227 Construct validity of measurements models 229 Discriminatory analysis and measurement model fit 235 Structural model fit 239 Validation of the model 243 Study two type 1 diabetes 244 Construct validity of measurements models 245 Discriminatory analysis and measurement model fit 247 Structural model fit 248 Discussion 252 Predictors of self-management 252 Structural constructs within the model of self-management 257 Chapter summary 259 PART 4: RESEARCH CONCLUSION 261 Chapter 9 DISCUSSION AND CONCLUSION OF THE STUDY 262 Chapter overview 263 Study summary 263 Integrative model of diabetes self-management 269 Model matching type 1 and type 2 275 Predictors of diabetes self-management 279 Implications of the study 286 Health care policy and practice 286 Health professional capacity 289 Self-management support 290 Theoretical implications 292 Strengths of the study 294 Integrated model of diabetes self-management 294 Statistical method 296 ix
Australian context 298 Limitations of the study 299 Methodology 299 Study instrument 301 Sampling issues 302 Future research 303 Closing comments 304 PART 5: SUPPLEMENTARY MATERIAL 306 References 307 Appendices 358 Appendix A 359 Illness representations in diabetes Appendix B 362 Study survey Appendix C 376 Participant information sheet Appendix D 377 Development and psychometric properties of scales Appendix E 390 Letter to distributors Appendix F 391 Study scales Appendix G 405 Ethical approval Appendix H 406 Confirmatory factor analyses Appendix I 418 Scale items retained for SEM Appendix J 421 Correlation matrix type 2 Appendix K 422 Structural models Appendix L 425 Correlation matrix type 1 x
Tables Table 4.1 Hypothesised determinants of self-management 103 Table 5.1 Study measurement instruments 112 Table 5.2 Summary of the scales and subscales reliability statistics 118 Table 6.1 Relationships between factors and self-efficacy 136 Table 6.2 Relationships between personal factors and locus of control 140 Table 6.3 Relationships between disease traits and locus of control 141 Table 6.4 Relationships between socio-environment and locus of control 143 Table 6.5 Relationships between health context and locus of control 144 Table 6.6 Relationships between personal factors / diabetes traits and diabetes 147 distress Table 6.7 Relationships between socio-environment / health context and 149 diabetes distress Table 6.8 Consultancy with the multidisciplinary diabetes care team 164 Table 6.9 Relationship between participant attributes and self-determination 169 support by health care professionals Table 6.10 Intercorrelations between dimensions in the Brief Illness Perception 172 Questionnaire Table 6.11 Relationship between personal attributes / diabetes traits and illness 175 representations Table 6.12 Relationship between socio-environment and illness representations 176 Table 6.13 Relationship between health context and illness representations 178 Table 6.14 Relationship between study factors and goal setting 181 Table 6.15 Relationship between study factors and appraisal/coping 182 Table 6.16 Study sample characteristics 187 Table 6.17 Table 7.1 Table 7.2 Table 7.3 Table 7.4 Table 7.5 Table 7.6 Table 7.7 Table 7.8 Summary of differences amongst sub-groups within each factors for each scales Relationship between diabetes management self-efficacy and selfmanagement Relationships between locus of control and self-management Relationships between diabetes distress and self-management Relationships between diabetes traits and self-management Relationships between diabetes co-morbidities and self-management Relationships between birthplace-related factors and selfmanagement Relationships between residency factors and self-management Relationships between marital status and self-management xi 188 193 194 195 197 198 201 202 203
Table 7.9 Relationships between occupation/education factors and selfmanagement 204 Table 7.10 Relationships between finances and self-management 205 Table 7.11 Relationships between diabetes care team access and selfmanagement 207 Table 7.12 Relationships between diabetes agencies and self-management 211 Table 7.13 Relationships between self-determination support and selfmanagement 212 Table 7.14 Relationship between self-efficacy and illness representations 214 Table 7.15 Relationship between self-efficacy and self-regulation 214 Table 7.16 Relationship between illness representations and self-regulation 215 Table 7.17 Relationship between illness representations and self-management 216 Table 7.18 Relationship between self-regulation and self-management 217 Table 7.19 Relationship between self-management and selfmanagement 218 outcomes Table 8.1 Summary of scale purification: Single-indicator latents for type 2 229 study group Table 8.2 Composite score formation for single-indicator latents for type 2 230 study group Table 8.3 Summary of scale purification: Multi-indicator latents for type 2 233 study group Table 8.4 Single indicator variables 234 Table 8.5 Correlation matrix for the measurement model - type 2 study group 238 Table 8.6 Mediation model for type 2 and DMSE 243 Table 8.7 Cross-validation statistics for the self-management model 244 Table 8.8 Summary of scale purification: Single-indicator latents for type 1 245 study group Table 8.9 Composite score formation for single-indicator latents for type 1 246 study group Table 8.10 Summary of scale purification: Multi-indicator latents for type 1 246 study group Table 8.11 Correlation matrix for the measurement model - type 1 study group 248 Table 8.12 Mediation model for type 1 and DMSE 251 Table 8.13 Predictors of self-management in type 1 and type 2 diabetes 252 Table 9.1 Determinants of diabetes self-management 280 Table 9.2 Determinants of self-management 281 Table A1 Summary characteristics and findings of diabetes studies related to 359 illness representation Table F1 Summary of the scales and subscales reliability statistics 396 Table I.1 Scale item retention for SEM 418 xii
Table J.1 Correlation matrix for the measurement model for type 2 421 Table L.1 Correlation matrix for the measurement model for type 1 425 xiii
Figures Figure 2.1 Wagner s Chronic Care Model 43 Figure 4.1 Biomedical influence on self-management 84 Figure 4.2 Behavioural influence on self-management 85 Figure 4.3 Socio-cognitive influence on self-management 88 Figure 4.4 Self-regulatory models influence on self-management 92 Figure 4.5 The parallel process model of self-regulation 93 Figure 4.6 The Common Sense Model s influence on self-management 96 Figure 4.7 Self-management model in diabetes: Model 1 97 Figure 4.8 Self-management model in diabetes: Model 2 97 Figure 4.9 Self-management model in diabetes: Model 3 98 Figure 4.10 Self-management model in diabetes: Model 4 99 Figure 4.11 Conceptual model of diabetes self-management 101 Figure 5.1 Health regions of Western Australia 106 Figure 6.1 Age and gender of participants 133 Figure 6.2 Item scores in the Diabetes Management Self-Efficacy Scale 135 Figure 6.3 Item scores for the Multidimensional Health Locus of Control scale 139 Figure 6.4 Item scores in the Diabetes Distress Scale 146 Figure 6.5 Types of diabetes according to gender of participants 151 Figure 6.6 Duration of diabetes 152 Figure 6.7 Diabetes related and non-specific co-morbidities 154 Figure 6.8 Therapeutic management 155 Figure 6.9 Health regions of Western Australia 157 Figure 6.10 Residency location within the health regions of Western Australia 158 Figure 6.11 Highest level of schooling based on residency location 159 Figure 6.12 Employment status of participants according to gender 160 Figure 6.13 Types of Government financial support 162 Figure 6.14 Year last attended a diabetes education programme 166 Figure 6.15 Item scores in the Health Care Climate Questionnaire 168 Figure 6.16 Dimension scores in the Brief Illness Perceptions Questionnaire 171 Figure 6.17 Causal categories of illness representations 173 Figure 6.18 Figure 6.19 Mean score for items in the setting and achieving diabetes goals subscale of the DES Mean score for items in the assessing dissatisfaction and readiness to change subscale of the DES xiv 179 180
Figure 6.20 Frequency of self-management 183 Figure 6.21 Last self-reported glycated haemoglobin 184 Figure 6.22 Quality of life ratings on the ADDQoL 19 186 Figure 8.1 Path diagram of the conceptual model for the study 226 Figure 8.2 Single indicator latent variable measurement model 230 Figure 8.3 Unidimensionality of parcelled diabetes distress variable 231 Figure 8.4 Unidimensionality of parcelled diabetes management self-efficacy 232 variable Figure 8.5 Unidimensionality of parcelled self-regulation variable 232 Figure 8.6 Measurement model for type 2 study group 237 Figure 8.7 Structural model of diabetes self-management - type 2 diabetes (v1) 240 Figure 8.8 Structural model of diabetes self-management - type 2 diabetes (v2) 241 Figure 8.9 Structural model of diabetes self-management - type 2 diabetes (v3) 241 Figure 8.10 Mediation model 243 Figure 8.11 Measurement model for type 1 study group 247 Figure 8.12 Structural model of diabetes self-management - type 1 (v1) 249 Figure 8.13 Structural model of diabetes self-management - type 1 (v2) 250 Figure 8.14 Structural models for people with type 1 and type 2 diabetes 258 Figure 9.1 Adjusted conceptual model 270 Figure 9.2 Comparison of type 1 and type 2 model 276 Figure 9.3 Final conceptual model of diabetes self-management 295 Figure F.1 Histogram for the ADDQoL 19 397 Figure F.2 Histogram for the BIPQ 398 Figure F.3 Histogram for the DDS 399 Figure F.4 Histogram for the DES 400 Figure F.5 Histogram for the DMSES 401 Figure F.6 Histogram for the HCCQ 401 Figure F.7 Histogram for the MHLC 403 Figure H.1 One factor congeneric model: DDe version 1 406 Figure H.2 One factor congeneric model: DDe final version 407 Figure H.3 One factor congeneric model: DDhcp 407 Figure H.4 One factor congeneric model: DDr 407 Figure H.5 One factor congeneric model: DDi version 1 408 Figure H.6 One factor congeneric model: DD1 final version 408 Figure H.7 One factor congeneric model: DMSEd version 1 409 xv
Figure H.8 One factor congeneric model: DMSEd final version 410 Figure H.9 One factor congeneric model: DMSEpa 410 Figure H.10 One factor congeneric model: DMSEbg 411 Figure H.11 One factor congeneric model: DMSEm 411 Figure H.12 Two factor congeneric model: DMSEbg and DMSEm 411 Figure H.13 One factor congeneric model: LOCdr 412 Figure H.14 One factor congeneric model: LOCi version 1 412 Figure H.15 One factor congeneric model: LOCi final version 413 Figure H.16 One factor congeneric model: SDS version 1 413 Figure H.17 One factor congeneric model: SDS final version 414 Figure H.18 One factor congeneric model: SRgs version 1 415 Figure H.19 One factor congeneric model: SRgs final version 415 Figure H.20 One factor congeneric model: SRa version 1 416 Figure H.21 Two factor congeneric model: SRa version 2 416 Figure H.22 Two factor congeneric model: SRa final version 417 Figure K.1 Structural model: DMSE 422 Figure K.2 Structural model: IR 423 Figure K.3 Structural model: SR 424 Figure K.4 Structural model: DSM 424 xvi