Assessments of functional improvement: self- versus clinician-ratings






Raymond W. LAM,MD



Vanessa C. EVANS,BSc
Mood and Anxiety Disorders Program
Department of Psychiatry
University of British Columbia
CANADA

Assessments of functional improvement: self- versus clinician-ratings


by V. C. Evans and R. W. Lam, Canada



Background: Impairment in psychosocial functioning, including social and occupational/role functioning, is common in individuals with depression, and improving functional outcomes should be an important goal of depression treatment. There are many standardized assessments of functioning available to help clinicians and researchers better measure and monitor functional outcomes, but these are employed much less frequently and consistently than symptom severity scales in clinical trials and clinical settings. Method: We review the issues and challenges in defining, measuring, and monitoring functional outcomes in depression, in particular the advantages and disadvantages of self- versus clinician-rated scales and other assessment methods. We also provide examples of validated assessments, with a focus on measures of occupational functioning, a particularly important outcome both for patients and society. Results: Psychosocial functioning outcomes are distinct from symptomatic and quality of life outcomes. They can be objective (ie, directly quantifiable), or more subjective (ie, based on patient perspectives) and captured through self-report and clinician ratings and observations, methods that offer distinct advantages and disadvantages. Selecting assessments depends on a number of factors, including psychometrics, reason for use, context, patient population, and setting. Conclusions: Improving functional outcomes begins with valid, reliable, and sensitive assessments that are appropriate for the purpose at hand. Fortunately, a wide range of tools are available. Such scales should be used to assess, monitor, and ultimately improve psychosocial outcomes in depression.

Medicographia. 2014;36:512-520 (see French abstract on page 520)



Improving functional outcomes is an important aspect of treatment in major mental disorders, both for individuals who experience illness-related functional impairment, and for society, which incurs significant direct and indirect costs of mental illness.1,2 Major depressive disorder (MDD) is one of the most common mental disorders3 and the second leading cause of disability worldwide.4 However, despite the personal and societal importance of psychosocial functioning in depression, functional outcomes have not received the same attention as symptomatic outcomes in either clinical or research settings. For example, although patients regard functional outcomes as most important to their recovery,5 assessments of functioning are not commonly used as primary or secondary outcomes in clinical trials.6,7 To ultimately improve functional outcomes in people with depression, it is obviously important to be able to feasibly and accurately assess patients’ level of functioning and to track any changes in functioning that occur over time (eg, with treatment, between episodes of depression, etc). A number of assessment tools have been developed and validated to assess functioning, both generally and in depression specifically. However, there is much variability in assessments, and there are many important considerations in selecting appropriate measures of functioning.

In this paper, we briefly review the issues surrounding defining, measuring, and monitoring functional outcomes in depression. We begin with a discussion of the differences between functional and symptomatic outcomes, quality of life, and “subjective” versus “objective” measures of functioning. Next, we outline some of the challenges in assessing functional outcomes in MDD, and the advantages and disadvantages of self- versus clinician-rated and other assessment methods. Finally, we describe some of the commonly used assessments of functioning in depression. Because of increasing clinical, research, and policy attention on depression in the workplace,8 we also highlight some assessments of occupational functioning.

What are functional outcomes and how are they different from symptom outcomes and quality of life?

Psychosocial functioning has been broadly defined as “one’s ability to perform the tasks of daily life and to engage in relationships with others in ways that are gratifying to the individual and others and that meet the needs of the community.”9

Within this definition, there are many ways to construe which domains of functioning constitute the “tasks of daily life” in a given society and culture. However, certain broad domains have been recurrently identified and evaluated in assessments of functioning; these include occupational or role (eg, student or other roles); household; social, including within the family (marital, parental, immediate, and extended),with friends, or in the community; leisure and recreational; self-care; and physical functioning.10





The core symptoms of depression, including affective (sad/low mood, anhedonia, guilt, low self-esteem), cognitive (eg, lack of motivation, difficulty with concentration, thinking, and memory, cognitive slowing), and somatic (changes in sleep, appetite) clusters, contribute substantially to psychosocial impairment in depression. However, although they are clearly related, functional status is not fully explained by the severity of depressive symptoms.11 For example, there is a variable range of correlations between scores on symptom and functioning scales in depression.12,13 Improvement in psychosocial functioning may lag behind symptomatic improvement6 and functional impairment may persist between episodes of depression, even during symptom remission.14,15 Although the causes of such persistent functional impairments are likely multifactorial and heterogeneous, contributing factors may include residual depressive and cognitive symptoms,16 medication side effects, psychiatric and medical comorbidities, and behavioral consequences of depression (eg, social isolation). Because functional improvement is not tightly correlated with symptomatic improvement, monitoring of outcomes in the treatment of depression should include assessment of both symptoms and functioning.

Another distinction is that between functioning and quality of life (QOL). Both are important and related concepts that are occasionally conflated or included under the umbrella of “psychosocial functioning.” The World Health Organization has described QOL as an “individual’s perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards and concerns.”17 That is, QOL is an inherently subjective measure based on self-perception and context with an emphasis on satisfaction, contentment, or enjoyment in various aspects of life. In contrast, functioning is more so understood to reflect one’s actual behavior in the world and assessed in ways that emphasize doing, performing, maintaining, etc.

An example of a QOL scale is the Medical Outcomes Study Health Survey–Short Form (SF-36).18 The SF-36 is a 36-item self-report scale that assesses health-related QOL and subjective health outcomes across different physical and mental health conditions. Although it is commonly referred to as a scale to assess functioning, the SF-36 only includes a few items on the impact of physical and mental health issues on activities of daily life that would be considered indicators of functioning. For the purposes of this paper, we will focus on functional measures and exclude discussion of QOL measures.

Assessment of functioning, however, can also be “subjective” (ie, relying on patients’ perceptions of their level of functioning) or “objective” (ie, directly quantifiable, eg, employment status, number of hours worked, frequency of attending social events, etc.).19 Subjective functional outcomes may be especially important in determining patient satisfaction and perspective for evaluating the success of treatment.


Table I
Table I. Advantages and disadvantages of different modalities to assess functioning in depression.

How do we assess functional outcomes in depression? Considerations, challenges, and differences among assessments of functioning

In addition to subjective versus objective measures, there are other considerations and challenges in assessing functional outcomes in depression that will inform the selection of assessments. One major consideration is the modality of evaluation— self-rated by the patient, clinician-rated based on patient report (usually with clinical or structured interviews), or observer-rated through direct observations or laboratory tasks. Table I summarizes the advantages and disadvantages of these modalities.

Self- and clinician-rated assessments can both be used to gather objective and subjective information about functioning. For example, the self-rated Social Functioning Scale (SFS),21 originally developed to assess social functioning in individuals with schizophrenia, includes items that would be considered both subjective (eg, “How easy do you find talking to people at the moment?”) and more “objective” (eg, frequency of participating in various social activities over the past three months, such as visiting relatives, visiting friends, playing an outdoor sport, etc). A major issue with self-rated instruments is the potential for respondent bias, especially given that depression is associated with negative self-perceptions. Clinician-rated assessments may have an advantage if clinical expertise is utilized to gain a more accurate evaluation of a patient’s actual level of functioning. However, clinician expertise and skill in interviewing varies, and even if structured or semi-structured interview guides are used, bias is still possible since they rely on a patient’s self-report during the interview. The drawback of clinician-rated assessments is the time and training required to complete them.

Direct task observation and laboratory tasks can minimize subjective bias, but these can be time-consuming and complicated and may be affected by other forms of depressive bias (eg, lack of motivation to participate in a task). One example of an observation-based task that has been used in schizophrenia and depression research is the Social Skills Performance Assessment (SSPA).22 Patients are scored on their performance in two brief, standardized role-play tasks: introducing oneself to a stranger and addressing an issue with a landlord.

Selection of functioning assessments
Selection of assessments will depend on a number of factors, including psychometrics, reason for use, context, patient population, and setting. All assessments need to demonstrate adequate psychometric properties, including consistency, validity, and reliability.

Some assessments are global, consisting of as few as one or two items that capture a patient’s overall level of functioning in, for example, work, household, and social domains, as in the Sheehan Disability Scale (SDS).23 Others assess multiple dimensions and may include several dozen items to collect more detailed information. The latter inevitably take longer and carry a greater burden for patients and clinicians to complete, but are necessary when the goal of the assessment is a more comprehensive understanding of functioning.

The purpose and context of the assessment will thus obviously affect the type of scale to be used. In research settings, more detailed and longer assessments are often necessary. For example, some scales are designed to capture theoretical constructs in psychosocial functioning, which generally include several dimensions, each requiring a number of items. In clinical trial settings, it is especially important that scales demonstrate sensitivity to change and ability to detect clinically important differences between treatments. In busy clinical settings, functional assessments must collect clinically relevant information to inform diagnosis and treatment decisions, and to monitor changes in functioning over time. Such scales need to be brief, acceptable to patients and clinicians, and easy to administer.20

Assessments must also be appropriate for the target population, so demographics and social and cultural context should be taken into account. Finally, scales vary by the time frame of assessment, ranging from the past week, the past month, to the past several months, which may also impact their utility. For a 6-week randomized controlled trial of an acute intervention for depression, a scale designed to assess functioning in the past month may be less sensitive to change than one assessing the past week.

In the following sections, we highlight some of the commonly used measures of functioning in depression, including global and multidimensional assessments and more specific assessments of social and occupational functioning.

Global and multidimensional assessments of psychosocial functioning

Many existing assessments of functioning are designed to evaluate more than one major domain of functioning, such as work/occupational, social, and household functioning, usually with one or two global items. There is a good range of self and clinician-rated options available, examples of which are listed and described in Table II (page 516-517). The advantage of such scales is to provide information on several important functional domains that may be differentially impaired, all within a single, brief scale.

Clinician-rated scales
With regard to clinician-rated global scales, the single-item Global Assessment of Functioning scale (GAF),29 which served as a measure of overall psychiatric disturbance and functioning (Axis V) of the DSM-III-R and DSM-IV, has been widely used in clinical settings. The GAF is flawed, however, as an assessment of functioning because it conflates symptoms with functioning. To address this limitation, the Social and Occupational Functioning Assessment Scale (SOFAS)28 was devised. The SOFAS is identical to the GAF except that the symptom components of the anchor points are removed, so that only functional impairment is assessed. The SOFAS is a single global score from 1 to 100, with lower scores indicating greater difficulties in functioning.

Other multidimensional assessments of functioning are more detailed than these global scales. For example, the clinician rated Multidimensional Scale of Independent Functioning (MSIF)25 assesses three different functional domains (work, household, and education, if applicable) by considering separately the degree of role responsibility, role support, and performance in each. These can be important factors in assessing functioning which are obscured in other global assessments.

The Longitudinal Interval Follow-up Evaluation–Range of Impaired Functioning Tool (LIFE-RIFT)24 is another multidimensional clinician-rated scale that is a good example of an assessment that incorporates items for both functioning and QOL. Validated for use in populations with MDD, the LIFERIFT scale assesses functioning in the domains of work (most impaired of: occupational, household, and educational functioning), interpersonal relations (most impaired relationship of: relationship with spouse, children, other relatives, or friends), recreation, and satisfaction, which is an item on global QOL.

Finally, in the new DSM-5, the World Health Organization’s Disability Assessment Schedule (WHODAS)30 has been recommended to replace the GAF as a routine assessment of functioning and disability. The WHODAS is available as 36- and 12-item versions with items on cognitive functioning, mobility, self-care, social, life activities (household and occupational/ educational functioning), and participation in the community. It is used across health conditions and mental disorders and can produce standardized disability scores, with general and clinical population norms also available. It is available in clinician- rated, self-rated, and proxy-rated formats.

Self-rated scales
There are a number of brief self-rated, global assessments of functioning as well. The Sheehan Disability Scale, described previously, and the Work and Social Adjustment Scale (WSAS),31 consisting of one item each on occupational, household, and social functioning, private leisure, and close relationships, are good examples of such scales.

One of the most widely-used assessments of psychosocial functioning in research studies is the Social Adjustment Scale (SAS),35 a 54-item self-report scale that looks at performance, interpersonal friction, and feelings and satisfaction in work (occupational, household, educational), and social (social, leisure activities, relationships with extended family, role as a marital partner, role as a parent, and role within the family unit) domains.

Another interesting multidimensional scale is available from the Patient Reported Outcome Measurement Information System (PROMIS).37 PROMIS is an initiative of several research centers that is funded by the US national Institutes of Health to provide highly reliable and valid assessments of patient-reported health, including physical, mental, and social well-being. Scales are standardized and comparisons are available across many different chronic health conditions, including depression. PROMIS has developed one self-report assessment of functioning, the “Ability to Participate in Social Roles and Activities” Short Form,32,33 which consists of 8 items assessing functioning in work (including occupational and household), social activities with family and friends, and leisure.

Assessments of occupational functioning

Most people with MDD experience impairments in their occupational functioning: they miss more days of work than those who are not depressed,38-40 and report being less productive when at work.41,42 Occupational functioning is obviously important to patients, who might fear or experience a loss of livelihood and attendant financial and social stress, and to employers, organizations, and society, which incur the costs of unemployment, long-term disability, absenteeism, and presenteeism.

Like other domains of functioning, assessment of work functioning and productivity can include objective (eg, hours of work missed) and subjective measures (eg, self-reported mistakes at work). Employment status, disability status, and time absent from work due to illness may appear to be more “objective” measures of work functioning than self-report measures of productivity. However, the former can be influenced by many external and corporate factors unrelated to illness, such as the availability of sick days, disability leave and insurance, flexibility in work hours, and accommodations at work, among others. While absenteeism can be used as an outcome measure in studies and clinical trials, there is often a skewed sample distribution.

There are also challenges in measuring productivity and presenteeism. It is difficult to objectively assess productivity based on units of output because these will vary widely across different occupations and will not be possible to quantify for many. For example, how is productivity measured objectively in physicians or nurses? Even when productivity output is quantifiable, important factors such as the amount of time or effort expended to produce that output may not be assessed.

Self-reports about performance at work are much more easily obtained and may be the only method to collect productivity information.43 However, subjective measures of productivity have their own unique measurement issues.44 For example, there are different methods to query productivity: by having respondents rate impairment directly, compare current performance to “usual” performance or the performance of an average worker in that role, estimate percentage of unproductive time at work, etc, all of which may assess slightly different constructs of presenteeism.


Table II
Table II. Examples of global and multidimensional
assessments of psychosocial functioning.

Abbreviations: MDD, major depressive disorder; OCD, obsessive
compulsive disorder; QOL, quality of life.

Table II


Also, few productivity and work functioning scales have been validated against objective measures (for a thorough discussion of these issues, see Brooks et al, 201044).

Work functioning scales
Notwithstanding these important issues, many existing assessments of occupational functioning, including absenteeism and presenteeism, are self-report scales. The majority are developed for use across various health conditions.

Table III lists examples of some of the common scales for occupational functioning. The World Health Organization’s Health and Work Performance Questionnaire (HPQ)46 is perhaps the “gold standard” assessment of occupational functioning. The HPQ is one of the few self-rated scales that has been validated against objective measures of productivity52 and used in large randomized controlled trials in MDD.53 However, at 44 items and 8-12 pages, it is too long to be practical for use in clinical settings.

The Work Limitations Questionnaire (WLQ)50 is another well researched and widely used assessment of presenteeism in chronic health conditions. The WLQ is available in a 25-item (full-length) version and a shortened 8-item version. Because it was developed to measure productivity across a range of general health conditions, it queries the impact of both physical health and emotional problems on functioning.

To fully capture the nature and extent of work impairment due to mental disorders such as depression, it may be necessary to use assessments of functioning specifically designed for that population. A recent review and comparison of productivity scales for use in mood disorders54 identified only two scales specifically validated in MDD: the Endicott Work Productivity Scale (EWPS)45 and the Lam Employment Absence and Productivity Scale (LEAPS).48 The LEAPS was developed to be a clinically useful measure of work impairment, assessing symptoms found to be most associated with occupational impairment in depression (eg, low energy or motivation, poor concentration or memory)55 as well as reduced work performance (eg, getting less work done, making more mistakes). It is sufficiently brief to be used in clinical settings but sensitive to changes with depression treatment.56


Table III
Table III. Examples of assessments of occupational functioning.

Conclusions

Functioning is important to individuals and to society. Impairment in functioning is a defining feature of MDD and psychiatric illnesses in general. Hence, functional outcomes must be assessed along with symptomatic and quality of life outcomes in research and treatment for depression. Improving functional outcomes begins with valid, reliable, and sensitive assessments of functioning that are appropriate for the purpose at hand. Fortunately, there is a wide range of tools available, from global and multidimensional assessments to detailed scales of specific domains such as social and occupational functioning.

When selecting a scale, clinicians and researchers must consider the type of information to be collected and the purpose of the assessment. Clinician-rated measures may provide additional information if the assessment is informed by clinical expertise, and laboratory paradigms can be useful in research settings. Assessments must demonstrate sensitivity to change if used for clinical trials. Brief, simple, patient-rated scales are usually most feasible for busy clinical settings. Used appropriately, assessments of functioning will serve as important tools for assessing, monitoring, and ultimately improving functional outcomes in depression. ■


References
1. Hu TW. Perspectives: an international review of the national cost estimates of mental illness, 1990-2003. J Ment Health Policy Econ. 2006;9(1):3-13.
2. Wittchen HU, Jacobi F, Rehm J, et al. The size and burden of mental disorders and other disorders of the brain in Europe 2010. Eur Neuropsychopharmacol. 2011;21(9):655-679.
3. Alonso J, Angermeyer MC, Bernert S, et al. Prevalence of mental disorders in Europe: results from the European Study of the Epidemiology of Mental Disorders (ESEMeD) project. Acta Psychiatr Scand Suppl. 2004(420):21-27.
4. The World Health Report 2004: Changing history, annex Table 3: Burden of disease in DALYs by cause, sex, and mortality stratum in WHO regions, estimates for 2002. Geneva, Switzerland: World Health Organization; 2004.
5. Zimmerman M, McGlinchey JB, Posternak MA, Friedman M, Attiullah n, Boerescu D. How should remission from depression be defined? The depressed patient’s perspective. Am J Psychiatry. 2006;163(1):148-150.
6. Bech P. Social functioning: should it become an endpoint in trials of antidepressants? CNS Drugs. 2005;19(4):313-324.
7. Lam RW, Filteau MJ, Milev R. Clinical effectiveness: the importance of psychosocial functioning outcomes. J Affect Disord. 2011;132(suppl 1):S9-S13.
8. Hughes S. Depression in the Workplace. Policy recommendations on how to tackle the leading cause of disability worldwide: European Parliament; 2014.
9. Michalak EE, Murray G. A clinician’s guide to psychosocial functioning and quality of life in bipolar disorder. In: Young AH, Ferrier nI, Michalak EE, eds. Practical Management of Bipolar Disorder. Cambridge, UK: Cambridge University Press; 2010.
10. Weirsma D, Becker T. Measuring social disabilities in mental health and employment outcomes. In: Thornicroft G, Tansella M, eds. Mental Health Outcomes Measures. 3rd ed; London, UK: Royal College of Psychiatrists; 2010:169-181.
11. Zimmerman M, McGlinchey JB, Posternak MA, Friedman M, Boerescu D, Attiullah n. Discordance between self-reported symptom severity and psychosocial functioning ratings in depressed outpatients: implications for how remission from depression should be defined. Psychiatry Res. 2006;141(2):185-191.
12. McKnight PE, Kashdan TB. The importance of functional impairment to mental health outcomes: a case for reassessing our goals in depression treatment research. Clin Psychol Rev. 2009;29(3):243-259.
13. Fried EI, nesse RM. The impact of individual depressive symptoms on impairment of psychosocial functioning. PLoS One. 2014;9(2):e90311.
14. Dewa CS, Thompson AH, Jacobs P. The association of treatment of depressive episodes and work productivity. Can J Psychiatry. 2011;56(12):743-750.
15. Greer TL, Kurian BT, Trivedi MH. Defining and measuring functional recovery from depression. CNS Drugs. 2010;24(4):267-284.
16. Romera I, Pérez V, Ciudad A, et al. Residual symptoms and functioning in depression, does the type of residual symptom matter? A post-hoc analysis. BMC Psychiatry. 2013;13:51.
17. The World Health Organization Quality of Life assessment (WHOQOL): position paper from the World Health Organization. Soc Sci Med. 1995;41(10):1403- 1409.
18. Ware JE, Sherbourne CD. The MOS 36-item short-form health survey (SF-36). I. Conceptual framework and item selection. Med Care. 1992;30(6):473-483.
19. Mintz J, Mintz LI, Arruda MJ, Hwang SS. Treatments of depression and the functional capacity to work. Arch Gen Psychiatry. 1992;49(10):761-768.
20. Zimmerman M. Tools for Depression: Standardized Rating Scales. 2011. Available at www.medscape.org/viewarticle/749921. Accessed February 12, 2014.
21. Birchwood M, Smith J, Cochrane R, Wetton S, Copestake S. The Social Functioning Scale. The development and validation of a new scale of social adjustment for use in family intervention programmes with schizophrenic patients. Br J Psychiatry. 1990;157:853-859.
22. Patterson TL, Moscona S, McKibbin CL, Davidson K, Jeste DV. Social skills performance assessment among older patients with schizophrenia. Schizophr Res. 2001;48(2-3):351-360.
23. Leon AC, Olfson M, Portera L, Farber L, Sheehan DV. Assessing psychiatric impairment in primary care with the Sheehan Disability Scale. Int J Psychiatry Med. 1997;27(2):93-105.
24. Leon AC, Solomon DA, Mueller TI, Turvey CL, Endicott J, Keller MB. The Range of Impaired Functioning Tool (LIFE-RIFT): a brief measure of functional impairment. Psychol Med. 1999;29(4):869-878.
25. Jaeger J, Berns SM, Czobor P. The multidimensional scale of independent functioning: a new instrument for measuring functional disability in psychiatric populations. Schizophr Bull. 2003;29(1):153-168.
26. Good-Ellis MA, Fine SB, Spencer JH, DiVittis A. Developing a Role Activity Performance Scale. Am J Occup Ther. 1987;41(4):232-241.
27. Goodman SH, Sewell DR, Cooley EL, Leavitt n. Assessing levels of adaptive functioning: the Role Functioning Scale. Community Ment Health J. 1993;29(2): 119-131.
28. Hilsenroth MJ, Ackerman SJ, Blagys MD, et al. Reliability and validity of DSM-IV axis V. Am J Psychiatry. 2000;157(11):1858-1863.
29. Endicott J, Spitzer R, Fleiss J, Cohen J. The global assessment scale: A procedure for measuring overall severity of psychiatric disturbance. Arch Gen Psychiatry. 1976;33:766-771.
30. Ustün TB, Chatterji S, Kostanjsek n, et al. Developing the World Health Organization Disability Assessment Schedule 2.0. Bull World Health Organ. 2010; 88(11):815-823.
31. Mundt JC, Marks IM, Shear MK, Greist JH. The Work and Social Adjustment Scale: a simple measure of impairment in functioning. Br J Psychiatry. 2002; 180:461-464.
32. Hahn EA, Devellis RF, Bode RK, et al. Measuring social health in the patientreported outcomes measurement information system (PROMIS): item bank development and testing. Qual Life Res. 2010;19(7):1035-1044.
33. Farin E, Ullrich A, Hauer J. Participation and social functioning in patients with fibromyalgia: development and testing of a new questionnaire. Health Qual Life Outcomes. 2013;11:135.
34. Bosc M, Dubini A, Polin V. Development and validation of a social functioning scale, the Social Adaptation Self-evaluation Scale. Eur Neuropsychopharmacol. 1997;7(suppl 1):S57-70; discussion S71-53.
35. Weissman MM, Bothwell S. Assessment of social adjustment by patient selfreport. Arch Gen Psychiatry. 1976;33(9):1111-1115.
36. Gupta M, Holshausen K, Best MW, et al. Relationships among neurocognition, symptoms, and functioning in treatment-resistant depression. Arch Clin Neuropsychol. 2013;28(3):272-281.
37. Cella D, Riley W, Stone A, et al. The Patient-Reported Outcomes Measurement Information System (PROMIS) developed and tested its first wave of adult self-reported health outcome item banks: 2005-2008. J Clin Epidemiol. 2010; 63(11):1179-1194.
38. Adler DA, McLaughlin TJ, Rogers WH, Chang H, Lapitsky L, Lerner D. Job performance deficits due to depression. Am J Psychiatry. 2006;163(9):1569- 1576.
39. Kessler RC, Barber C, Birnbaum HG, et al. Depression in the workplace: effects on short-term disability. Health Aff (Millwood). 1999;18(5):163-171.
40. Kessler RC, Akiskal HS, Ames M, et al. Prevalence and effects of mood disorders on work performance in a nationally representative sample of U.S. workers. Am J Psychiatry. 2006;163(9):1561-1568.
41. Johnston K, Westerfield W, Momin S, Phillippi R, naidoo A. The direct and indirect costs of employee depression, anxiety, and emotional disorders—an employer case study. J Occup Environ Med. 2009;51(5):564-577.
42. Stewart WF, Ricci JA, Chee E, Hahn SR, Morganstein D. Cost of lost productive work time among US workers with depression. JAMA. 2003;289(23):3135- 3144.
43. Schultz AB, Chen CY, Edington DW. The cost and impact of health conditions on presenteeism to employers: a review of the literature. Pharmacoeconomics. 2009;27(5):365-378.
44. Brooks A, Hagen SE, Sathyanarayanan S, Schultz AB, Edington DW. Presenteeism: critical issues. J Occup Environ Med. 2010; 52(11):1055-1067.
45. Endicott J, nee J. Endicott Work Productivity Scale (EWPS): a new measure to assess treatment effects. Psychopharmacol Bull. 1997;33(1):13-16.
46. Kessler RC, Barber C, Beck A, et al. The World Health Organization Health and Work Performance Questionnaire (HPQ). J Occup Environ Med. 2003;45(2): 156-174.
47. van Roijen L, Essink-Bot ML, Koopmanschap MA, Bonsel G, Rutten FF. Labor and health status in economic evaluation of health care. The Health and Labor Questionnaire. Int J Technol Assess Health Care. 1996;12(3):405-415.
48. Lam RW, Michalak EE, Yatham Ln. A new clinical rating scale for work absence and productivity: validation in patients with major depressive disorder. BMC Psychiatry. 2009;9:78.
49. Koopman C, Pelletier KR, Murray JF, et al. Stanford presenteeism scale: health status and employee productivity. J Occup Environ Med. 2002;44(1):14-20.
50. Lerner D, Amick BC, Rogers WH, Malspeis S, Bungay K, Cynn D. The Work Limitations Questionnaire. Med Care. 2001;39(1):72-85.
51. Beck A, Crain AL, Solberg LI, et al. Severity of depression and magnitude of productivity loss. Ann Fam Med. 2011;9(4):305-311.
52. Allen HM, Bunn WB. Validating self-reported measures of productivity at work: a case for their credibility in a heavy manufacturing setting. J Occup Environ Med. 2003;45(9):926-940.
53. Wang PS, Simon GE, Avorn J, et al. Telephone screening, outreach, and care management for depressed workers and impact on clinical and work productivity outcomes: a randomized controlled trial. JAMA. 2007;298(12):1401-1411.
54. Despiégel n, Danchenko n, François C, Lensberg B, Drummond MF. The use and performance of productivity scales to evaluate presenteeism in mood disorders. Value Health. 2012;15(8):1148-1161.
55. Lam RW, Michalak EE, Bond DJ, Tam EM, Axler A, Yatham Ln. Which depressive symptoms and medication side effects are perceived by patients as interfering most with occupational functioning? Depress Res Treat. 2012;2012: 630206.
56. Lam RW, Parikh SV, Ramasubbu R, et al. Effects of combined pharmacotherapy and psychotherapy for improving work functioning in major depressive disorder. Br J Psychiatry. 2013;203(5):358-365.


Keywords: assessment; major depression; occupational functioning outcome; psychosocial functioning outcome