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Improving Depression Care: Barriers, Solutions, and Research Needs
The barriers to improving care of depressive illness are well known. Patients resist mental disorder diagnoses, are not ready to accept treatment, or fail to follow through on prescribed treatments. Primary care physicians fail to recognize depression in their patients, fail to prescribe an adequate treatment regimen, or fail to follow-up with patients once treatment is initiated. Psychiatrists and other mental health professionals are not accessible to many depressed individuals (elderly, rural, medically ill, and economically disadvantaged populations). Health care systems often fail to organize mental health consultation services to support the work of primary care physicians who treat the majority of depressed patients. Insurers and employers resist adequate insurance benefits for mental health services. Given the extent and complexity of the barriers to improved care of depressive illness, it is not surprising that little progress has been made in reducing the burden of depressive illness on a population basis, despite the availability of effective treatments. The problem is not lack of effective treatments for depression but deficiencies in the organization and delivery of health and mental health services.
Although understanding the barriers to improved care is important, focusing on barriers alone can be contagious and counterproductive. The litany of barriers can easily become a rationale for inaction. Bringing potential solutions to light provides an invitation to experiment, try things out, and take action.
At our conference on improving care for depression in organized health care systems, current experimental research was presented in which possible approaches to improving care of depressive illness were tested and effects on patient outcomes were assessed. After the research presentations the participants (eg, leading researchers and persons responsible for improving the quality of care for mental disorders in systems serving of millions of people) identified possible solutions to the well-known barriers to improved depression care.
Barriers and solutions are listed in the Table 1 using the framework of the Model for Improving Chronic Illness Care described elsewhere.1 In each area we enumerate barriers and potential solutions identified by the conference participants. In the final analysis, the most significant barrier to improving the quality of care for depressive illness may be inaction, because all other barriers are insurmountable in the absence of effort to produce change.
Research needs
The conference participants also considered research needs that have not been adequately addressed by the current generation of depression research.
Case Management
The current generation of depression care studies has tested different forms of case management with generally promising results. Critical unresolved questions focus on whom case management services are needed for and how long it should be sustained. Some research suggests that case management services may need to be continued over long periods of time, but outcome data beyond 1 year are lacking. Additional research is needed to clarify the benefits of having specialist-consultants both supervise the work of case managers and provide services targeted to patients who do not achieve a favorable outcome with case management services alone. Although case managers have been used most frequently in support of pharmacotherapy, it remains unclear to what extent patients benefit from the behavioral and supportive interventions they provide. To what extent do case management services benefit patients through mobilization of hope and behavioral activation versus improved adherence to treatment regimens? Should these services be delivered by depression case managers who follow a large caseload of depressed primary care patients, or should depression be one of many chronic conditions such as diabetes, hypertension, and asthma that are managed by a generalist case manager working as part of the primary care team? Also, there is a need for development and testing of new modes of delivering case management services in addition to in-person and telephonic services (eg, telemedicine services or the Internet). New approaches are needed to increase the feasibility of sustained case management and to reduce costs.
Research in New Populations
A logical next step is to test the care models proven useful for depressed patients in diverse patient populations. Research on care of other common psychiatric illnesses such as anxiety disorders, somatoform disorders, and bipolar disorder is needed. Adapting the new care models and testing their effectiveness in the care of rural, economically disadvantaged, and elderly populations would also be useful. Future research might test provision of case management and specialist consultation services through telemedicine connections for patient populations lacking direct access to such services in their primary care setting (eg, rural practices, network model practices). Finally, the management of treatment-resistant patients was identified as a critically important issue that has not been resolved. Will treatment-resistant patients benefit more from referral for specialty mental health care, or can they be effectively managed in the primary care setting with effective organization of treatment and support services? Surprisingly little is known about the care of depression among patients with comorbid medical disease (eg, diabetes, heart disease, chronic obstructive pulmonary disease). There is now substantial evidence that depression is associated with increased physical symptoms, increased disability, increased use of general medical services, and increased likelihood of comorbid medical illness.2 Enrolling patients with a specific chronic disease such as diabetes or coronary artery disease would enable researchers to more precisely delineate the effect of improved depression care on biologic measures of disease severity as well as physical symptoms, disability, and use of health care services. The impact of improved depression care on the ability of patients to manage a comorbid chronic disease is of considerable interest.
Stepped Care and Relapse Prevention
An emerging theme in the current generation of depression care research is the use of sequential or stepped care management strategies. In stepped care interventions, patient outcomes are monitored, and modifications in the care plan and/or more intensive management are targeted toward patients who do not have a favorable outcome by a defined time point (eg, 2 months after the initiation of treatment).3,4 It is hoped that stepped care models will enhance the cost-effectiveness of depression care programs by reserving the use of case management and specialist consultation services for those patients who cannot be effectively managed by the primary care physician alone. In general, there is a need for new research (and analyses from completed studies) that identify ways of using limited specialist and case management services to greatest effect in improving the long-term outcomes per unit cost. Effectiveness studies now need to develop and test interventions that follow patients for continuation and maintenance phases to assess their ability to prevent relapse and maximize patient functioning over extended periods of time.
Societal Benefits of Improved Depression Care
There was a sense of urgency about the need for new research that more adequately assesses the effects of treating depression on labor force participation, market and nonmarket productivity, work absenteeism, family functioning, and time off work for travel to mental health treatments. The need to evaluate the effects of treating depression on both the depressed individual and members of their families was recognized. Research in these important areas has been hampered by the lack of reliable and valid measures. In particular, the development of reliable and valid measures of work productivity and family burden were seen as critically important.
Expert panels have recommended that alternative treatments be compared using cost utility methods that explicitly incorporate patient outcome preferences.5 The evaluation of health state preferences remains uncommon in depression clinical trials because of measurement problems. Different research groups have recently attempted to indirectly measure how patient utilities vary with different dimensions of health quality of life using the 12-item Medical Outcomes Study Short Form or the 36-item Medical Outcomes Study Short Form.6-9 However, the validity of these alternative approaches is unclear. Resolution of these uncertainties was considered to be an important research area.
Multisite Trials and Meta-Analytic Approaches
As depression research increasingly focuses on assessing effects on societal costs and benefits of improved depression care, the large variance of policy-relevant outcome measures such as disability days, unemployment, and health care costs is of increasing concern. Effectiveness studies enrolling even 200 to 300 patients are underpowered to detect clinically significant differences in many of these outcomes,10 even though even modest beneficial effects of treatment could have substantial social significance on a population basis. This suggests the need for large-scale multisite trials of depression care programs. The effects of depression care programs on these outcomes might also be assessed through meta-analyses of completed trials or new intervention studies that are designed to vary components of the intervention strategy.
Conclusions
Completed trials suggest that depression care programs integrated into the primary care setting can improve depression and disability outcomes of patients with major and possibly minor depression. The completed research increases the public health imperative for refining understanding of how to provide depression care most effectively and cost-effectively and for determining the extent to which these interventions can benefit new patient populations and the societal benefits of such care programs. The completed trials have established a stronger basis for organized efforts to improve the quality of depression care in health care systems. They have also set the stage for both larger trials and meta-analyses of completed trials that are designed to answer key questions about the societal benefits of improved depression care.
1. Wagner EH, Austin BT, Von Korff M. Organizing care for patients with chronic illness. Milbank Q 1996;74:511-44.
2. Katon W. The effect of major depression on chronic medical illness. Clin Neuropsychiatry 1998;3:82-86.
3. Katon W, Von Korff M, Lin E, et al. Population-based care of depression: effective disease management strategies to decrease prevalence. Gen Hosp Psychiatry 1997;19:169-78.
4. Von Korff M, Tiemens B. Individualized stepped care of chronic illness. West J Med 2000;172:133-37.
5. Gold MR. Siegel JE, Russel LB, Weinstein MC, eds Cost-effectiveness in health and Medicare. New York, NY: Oxford University Press; 1996.
6. Sherbourne CD, Sturm R, Wells KB. What outcomes matter to patients? J Gen Intern Med 1999;14:357-63.
7. Brazier J, Usherwood T, Harper R, Thomas K. Deriving a preference-based single index from the UK SF-36 Health Survey. J Clin Epidemiol 1998;51:1115-28.
8. Sugar CA, Sturm R, Lee TT, et al. Empirically defined health states for depression from the SF-12. Health Serv Res 1998;33:911-28.
9. Fryback DG, Lawrence WF, Martin PA, et al. Predicting quality of wellbeing scores from the SF-36 results from the Beaver Dam Health Outcomes Study. Med Decis Making 1997;17:1-9.
10. Sturm R, Unützer J, Katon W. Effectiveness research and implications for study design: sample size and statistical power. Gen Hosp Psychiatry 1999;21:274-83.
The barriers to improving care of depressive illness are well known. Patients resist mental disorder diagnoses, are not ready to accept treatment, or fail to follow through on prescribed treatments. Primary care physicians fail to recognize depression in their patients, fail to prescribe an adequate treatment regimen, or fail to follow-up with patients once treatment is initiated. Psychiatrists and other mental health professionals are not accessible to many depressed individuals (elderly, rural, medically ill, and economically disadvantaged populations). Health care systems often fail to organize mental health consultation services to support the work of primary care physicians who treat the majority of depressed patients. Insurers and employers resist adequate insurance benefits for mental health services. Given the extent and complexity of the barriers to improved care of depressive illness, it is not surprising that little progress has been made in reducing the burden of depressive illness on a population basis, despite the availability of effective treatments. The problem is not lack of effective treatments for depression but deficiencies in the organization and delivery of health and mental health services.
Although understanding the barriers to improved care is important, focusing on barriers alone can be contagious and counterproductive. The litany of barriers can easily become a rationale for inaction. Bringing potential solutions to light provides an invitation to experiment, try things out, and take action.
At our conference on improving care for depression in organized health care systems, current experimental research was presented in which possible approaches to improving care of depressive illness were tested and effects on patient outcomes were assessed. After the research presentations the participants (eg, leading researchers and persons responsible for improving the quality of care for mental disorders in systems serving of millions of people) identified possible solutions to the well-known barriers to improved depression care.
Barriers and solutions are listed in the Table 1 using the framework of the Model for Improving Chronic Illness Care described elsewhere.1 In each area we enumerate barriers and potential solutions identified by the conference participants. In the final analysis, the most significant barrier to improving the quality of care for depressive illness may be inaction, because all other barriers are insurmountable in the absence of effort to produce change.
Research needs
The conference participants also considered research needs that have not been adequately addressed by the current generation of depression research.
Case Management
The current generation of depression care studies has tested different forms of case management with generally promising results. Critical unresolved questions focus on whom case management services are needed for and how long it should be sustained. Some research suggests that case management services may need to be continued over long periods of time, but outcome data beyond 1 year are lacking. Additional research is needed to clarify the benefits of having specialist-consultants both supervise the work of case managers and provide services targeted to patients who do not achieve a favorable outcome with case management services alone. Although case managers have been used most frequently in support of pharmacotherapy, it remains unclear to what extent patients benefit from the behavioral and supportive interventions they provide. To what extent do case management services benefit patients through mobilization of hope and behavioral activation versus improved adherence to treatment regimens? Should these services be delivered by depression case managers who follow a large caseload of depressed primary care patients, or should depression be one of many chronic conditions such as diabetes, hypertension, and asthma that are managed by a generalist case manager working as part of the primary care team? Also, there is a need for development and testing of new modes of delivering case management services in addition to in-person and telephonic services (eg, telemedicine services or the Internet). New approaches are needed to increase the feasibility of sustained case management and to reduce costs.
Research in New Populations
A logical next step is to test the care models proven useful for depressed patients in diverse patient populations. Research on care of other common psychiatric illnesses such as anxiety disorders, somatoform disorders, and bipolar disorder is needed. Adapting the new care models and testing their effectiveness in the care of rural, economically disadvantaged, and elderly populations would also be useful. Future research might test provision of case management and specialist consultation services through telemedicine connections for patient populations lacking direct access to such services in their primary care setting (eg, rural practices, network model practices). Finally, the management of treatment-resistant patients was identified as a critically important issue that has not been resolved. Will treatment-resistant patients benefit more from referral for specialty mental health care, or can they be effectively managed in the primary care setting with effective organization of treatment and support services? Surprisingly little is known about the care of depression among patients with comorbid medical disease (eg, diabetes, heart disease, chronic obstructive pulmonary disease). There is now substantial evidence that depression is associated with increased physical symptoms, increased disability, increased use of general medical services, and increased likelihood of comorbid medical illness.2 Enrolling patients with a specific chronic disease such as diabetes or coronary artery disease would enable researchers to more precisely delineate the effect of improved depression care on biologic measures of disease severity as well as physical symptoms, disability, and use of health care services. The impact of improved depression care on the ability of patients to manage a comorbid chronic disease is of considerable interest.
Stepped Care and Relapse Prevention
An emerging theme in the current generation of depression care research is the use of sequential or stepped care management strategies. In stepped care interventions, patient outcomes are monitored, and modifications in the care plan and/or more intensive management are targeted toward patients who do not have a favorable outcome by a defined time point (eg, 2 months after the initiation of treatment).3,4 It is hoped that stepped care models will enhance the cost-effectiveness of depression care programs by reserving the use of case management and specialist consultation services for those patients who cannot be effectively managed by the primary care physician alone. In general, there is a need for new research (and analyses from completed studies) that identify ways of using limited specialist and case management services to greatest effect in improving the long-term outcomes per unit cost. Effectiveness studies now need to develop and test interventions that follow patients for continuation and maintenance phases to assess their ability to prevent relapse and maximize patient functioning over extended periods of time.
Societal Benefits of Improved Depression Care
There was a sense of urgency about the need for new research that more adequately assesses the effects of treating depression on labor force participation, market and nonmarket productivity, work absenteeism, family functioning, and time off work for travel to mental health treatments. The need to evaluate the effects of treating depression on both the depressed individual and members of their families was recognized. Research in these important areas has been hampered by the lack of reliable and valid measures. In particular, the development of reliable and valid measures of work productivity and family burden were seen as critically important.
Expert panels have recommended that alternative treatments be compared using cost utility methods that explicitly incorporate patient outcome preferences.5 The evaluation of health state preferences remains uncommon in depression clinical trials because of measurement problems. Different research groups have recently attempted to indirectly measure how patient utilities vary with different dimensions of health quality of life using the 12-item Medical Outcomes Study Short Form or the 36-item Medical Outcomes Study Short Form.6-9 However, the validity of these alternative approaches is unclear. Resolution of these uncertainties was considered to be an important research area.
Multisite Trials and Meta-Analytic Approaches
As depression research increasingly focuses on assessing effects on societal costs and benefits of improved depression care, the large variance of policy-relevant outcome measures such as disability days, unemployment, and health care costs is of increasing concern. Effectiveness studies enrolling even 200 to 300 patients are underpowered to detect clinically significant differences in many of these outcomes,10 even though even modest beneficial effects of treatment could have substantial social significance on a population basis. This suggests the need for large-scale multisite trials of depression care programs. The effects of depression care programs on these outcomes might also be assessed through meta-analyses of completed trials or new intervention studies that are designed to vary components of the intervention strategy.
Conclusions
Completed trials suggest that depression care programs integrated into the primary care setting can improve depression and disability outcomes of patients with major and possibly minor depression. The completed research increases the public health imperative for refining understanding of how to provide depression care most effectively and cost-effectively and for determining the extent to which these interventions can benefit new patient populations and the societal benefits of such care programs. The completed trials have established a stronger basis for organized efforts to improve the quality of depression care in health care systems. They have also set the stage for both larger trials and meta-analyses of completed trials that are designed to answer key questions about the societal benefits of improved depression care.
The barriers to improving care of depressive illness are well known. Patients resist mental disorder diagnoses, are not ready to accept treatment, or fail to follow through on prescribed treatments. Primary care physicians fail to recognize depression in their patients, fail to prescribe an adequate treatment regimen, or fail to follow-up with patients once treatment is initiated. Psychiatrists and other mental health professionals are not accessible to many depressed individuals (elderly, rural, medically ill, and economically disadvantaged populations). Health care systems often fail to organize mental health consultation services to support the work of primary care physicians who treat the majority of depressed patients. Insurers and employers resist adequate insurance benefits for mental health services. Given the extent and complexity of the barriers to improved care of depressive illness, it is not surprising that little progress has been made in reducing the burden of depressive illness on a population basis, despite the availability of effective treatments. The problem is not lack of effective treatments for depression but deficiencies in the organization and delivery of health and mental health services.
Although understanding the barriers to improved care is important, focusing on barriers alone can be contagious and counterproductive. The litany of barriers can easily become a rationale for inaction. Bringing potential solutions to light provides an invitation to experiment, try things out, and take action.
At our conference on improving care for depression in organized health care systems, current experimental research was presented in which possible approaches to improving care of depressive illness were tested and effects on patient outcomes were assessed. After the research presentations the participants (eg, leading researchers and persons responsible for improving the quality of care for mental disorders in systems serving of millions of people) identified possible solutions to the well-known barriers to improved depression care.
Barriers and solutions are listed in the Table 1 using the framework of the Model for Improving Chronic Illness Care described elsewhere.1 In each area we enumerate barriers and potential solutions identified by the conference participants. In the final analysis, the most significant barrier to improving the quality of care for depressive illness may be inaction, because all other barriers are insurmountable in the absence of effort to produce change.
Research needs
The conference participants also considered research needs that have not been adequately addressed by the current generation of depression research.
Case Management
The current generation of depression care studies has tested different forms of case management with generally promising results. Critical unresolved questions focus on whom case management services are needed for and how long it should be sustained. Some research suggests that case management services may need to be continued over long periods of time, but outcome data beyond 1 year are lacking. Additional research is needed to clarify the benefits of having specialist-consultants both supervise the work of case managers and provide services targeted to patients who do not achieve a favorable outcome with case management services alone. Although case managers have been used most frequently in support of pharmacotherapy, it remains unclear to what extent patients benefit from the behavioral and supportive interventions they provide. To what extent do case management services benefit patients through mobilization of hope and behavioral activation versus improved adherence to treatment regimens? Should these services be delivered by depression case managers who follow a large caseload of depressed primary care patients, or should depression be one of many chronic conditions such as diabetes, hypertension, and asthma that are managed by a generalist case manager working as part of the primary care team? Also, there is a need for development and testing of new modes of delivering case management services in addition to in-person and telephonic services (eg, telemedicine services or the Internet). New approaches are needed to increase the feasibility of sustained case management and to reduce costs.
Research in New Populations
A logical next step is to test the care models proven useful for depressed patients in diverse patient populations. Research on care of other common psychiatric illnesses such as anxiety disorders, somatoform disorders, and bipolar disorder is needed. Adapting the new care models and testing their effectiveness in the care of rural, economically disadvantaged, and elderly populations would also be useful. Future research might test provision of case management and specialist consultation services through telemedicine connections for patient populations lacking direct access to such services in their primary care setting (eg, rural practices, network model practices). Finally, the management of treatment-resistant patients was identified as a critically important issue that has not been resolved. Will treatment-resistant patients benefit more from referral for specialty mental health care, or can they be effectively managed in the primary care setting with effective organization of treatment and support services? Surprisingly little is known about the care of depression among patients with comorbid medical disease (eg, diabetes, heart disease, chronic obstructive pulmonary disease). There is now substantial evidence that depression is associated with increased physical symptoms, increased disability, increased use of general medical services, and increased likelihood of comorbid medical illness.2 Enrolling patients with a specific chronic disease such as diabetes or coronary artery disease would enable researchers to more precisely delineate the effect of improved depression care on biologic measures of disease severity as well as physical symptoms, disability, and use of health care services. The impact of improved depression care on the ability of patients to manage a comorbid chronic disease is of considerable interest.
Stepped Care and Relapse Prevention
An emerging theme in the current generation of depression care research is the use of sequential or stepped care management strategies. In stepped care interventions, patient outcomes are monitored, and modifications in the care plan and/or more intensive management are targeted toward patients who do not have a favorable outcome by a defined time point (eg, 2 months after the initiation of treatment).3,4 It is hoped that stepped care models will enhance the cost-effectiveness of depression care programs by reserving the use of case management and specialist consultation services for those patients who cannot be effectively managed by the primary care physician alone. In general, there is a need for new research (and analyses from completed studies) that identify ways of using limited specialist and case management services to greatest effect in improving the long-term outcomes per unit cost. Effectiveness studies now need to develop and test interventions that follow patients for continuation and maintenance phases to assess their ability to prevent relapse and maximize patient functioning over extended periods of time.
Societal Benefits of Improved Depression Care
There was a sense of urgency about the need for new research that more adequately assesses the effects of treating depression on labor force participation, market and nonmarket productivity, work absenteeism, family functioning, and time off work for travel to mental health treatments. The need to evaluate the effects of treating depression on both the depressed individual and members of their families was recognized. Research in these important areas has been hampered by the lack of reliable and valid measures. In particular, the development of reliable and valid measures of work productivity and family burden were seen as critically important.
Expert panels have recommended that alternative treatments be compared using cost utility methods that explicitly incorporate patient outcome preferences.5 The evaluation of health state preferences remains uncommon in depression clinical trials because of measurement problems. Different research groups have recently attempted to indirectly measure how patient utilities vary with different dimensions of health quality of life using the 12-item Medical Outcomes Study Short Form or the 36-item Medical Outcomes Study Short Form.6-9 However, the validity of these alternative approaches is unclear. Resolution of these uncertainties was considered to be an important research area.
Multisite Trials and Meta-Analytic Approaches
As depression research increasingly focuses on assessing effects on societal costs and benefits of improved depression care, the large variance of policy-relevant outcome measures such as disability days, unemployment, and health care costs is of increasing concern. Effectiveness studies enrolling even 200 to 300 patients are underpowered to detect clinically significant differences in many of these outcomes,10 even though even modest beneficial effects of treatment could have substantial social significance on a population basis. This suggests the need for large-scale multisite trials of depression care programs. The effects of depression care programs on these outcomes might also be assessed through meta-analyses of completed trials or new intervention studies that are designed to vary components of the intervention strategy.
Conclusions
Completed trials suggest that depression care programs integrated into the primary care setting can improve depression and disability outcomes of patients with major and possibly minor depression. The completed research increases the public health imperative for refining understanding of how to provide depression care most effectively and cost-effectively and for determining the extent to which these interventions can benefit new patient populations and the societal benefits of such care programs. The completed trials have established a stronger basis for organized efforts to improve the quality of depression care in health care systems. They have also set the stage for both larger trials and meta-analyses of completed trials that are designed to answer key questions about the societal benefits of improved depression care.
1. Wagner EH, Austin BT, Von Korff M. Organizing care for patients with chronic illness. Milbank Q 1996;74:511-44.
2. Katon W. The effect of major depression on chronic medical illness. Clin Neuropsychiatry 1998;3:82-86.
3. Katon W, Von Korff M, Lin E, et al. Population-based care of depression: effective disease management strategies to decrease prevalence. Gen Hosp Psychiatry 1997;19:169-78.
4. Von Korff M, Tiemens B. Individualized stepped care of chronic illness. West J Med 2000;172:133-37.
5. Gold MR. Siegel JE, Russel LB, Weinstein MC, eds Cost-effectiveness in health and Medicare. New York, NY: Oxford University Press; 1996.
6. Sherbourne CD, Sturm R, Wells KB. What outcomes matter to patients? J Gen Intern Med 1999;14:357-63.
7. Brazier J, Usherwood T, Harper R, Thomas K. Deriving a preference-based single index from the UK SF-36 Health Survey. J Clin Epidemiol 1998;51:1115-28.
8. Sugar CA, Sturm R, Lee TT, et al. Empirically defined health states for depression from the SF-12. Health Serv Res 1998;33:911-28.
9. Fryback DG, Lawrence WF, Martin PA, et al. Predicting quality of wellbeing scores from the SF-36 results from the Beaver Dam Health Outcomes Study. Med Decis Making 1997;17:1-9.
10. Sturm R, Unützer J, Katon W. Effectiveness research and implications for study design: sample size and statistical power. Gen Hosp Psychiatry 1999;21:274-83.
1. Wagner EH, Austin BT, Von Korff M. Organizing care for patients with chronic illness. Milbank Q 1996;74:511-44.
2. Katon W. The effect of major depression on chronic medical illness. Clin Neuropsychiatry 1998;3:82-86.
3. Katon W, Von Korff M, Lin E, et al. Population-based care of depression: effective disease management strategies to decrease prevalence. Gen Hosp Psychiatry 1997;19:169-78.
4. Von Korff M, Tiemens B. Individualized stepped care of chronic illness. West J Med 2000;172:133-37.
5. Gold MR. Siegel JE, Russel LB, Weinstein MC, eds Cost-effectiveness in health and Medicare. New York, NY: Oxford University Press; 1996.
6. Sherbourne CD, Sturm R, Wells KB. What outcomes matter to patients? J Gen Intern Med 1999;14:357-63.
7. Brazier J, Usherwood T, Harper R, Thomas K. Deriving a preference-based single index from the UK SF-36 Health Survey. J Clin Epidemiol 1998;51:1115-28.
8. Sugar CA, Sturm R, Lee TT, et al. Empirically defined health states for depression from the SF-12. Health Serv Res 1998;33:911-28.
9. Fryback DG, Lawrence WF, Martin PA, et al. Predicting quality of wellbeing scores from the SF-36 results from the Beaver Dam Health Outcomes Study. Med Decis Making 1997;17:1-9.
10. Sturm R, Unützer J, Katon W. Effectiveness research and implications for study design: sample size and statistical power. Gen Hosp Psychiatry 1999;21:274-83.