The importance of functional impairment to mental health outcomes: A case for reassessing our goals in depression treatment research

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Abstract

Outcomes in depression treatment research include both changes in symptom severity and functional impairment. Symptom measures tend to be the standard outcome but we argue that there are benefits to considering functional outcomes. An exhaustive literature review shows that the relationship between symptoms and functioning remains unexpectedly weak and often bidirectional. Changes in functioning often lag symptom changes. As a result, functional outcomes might offer depression researchers more critical feedback and better guidance when studying depression treatment outcomes. The paper presents a case for the necessity of both functional and symptom outcomes in depression treatment research by addressing three aims—1) review the research relating symptoms and functioning, 2) provide a rationale for measuring both outcomes, and 3) discuss potential artifacts in measuring functional outcomes. The three aims are supported by an empirical review of the treatment outcome and epidemiological literatures.

Introduction

Mental disorders create societal problems because they produce functional impairment. These impairments may either cause or be caused by the disorder (see Barnett & Gotlib, 1988); regardless of the causal properties, there must be a link between impairment and disorder for researchers, policy-makers, and health care professionals to pay attention.1 If functional impairment potentially drives our attention then functional impairment ought to be a prominent outcome for evaluating treatments. A cursory review of psychological and psychiatric treatment outcome literature suggests otherwise. A systematic search of over 90 depression treatment outcome meta-analyses indicates that less than 5% of the clinical trials measure and report functional outcomes. That cursory review corroborates a systematic review of more than 150 published depression clinical trials where an even lower proportion reported any functional outcomes. The most prominent outcomes consist of symptoms, symptom profiles, or diagnostic endpoints. Measuring symptom outcomes makes sense; symptoms are the most proximal indicators of a disorder. Unfortunately, these indicators only take us so far. We can examine whether people with disorders possess different symptom scores or profiles before and after treatment. What remains unanswered is whether these measures provide us with an understanding of functional change – that is, whether people are more functionally capable after treatment.

Symptom measures somewhat reflect functional impairment but lack domain-specific functional information. As a result, depression researchers acknowledge the need for multidimensional outcomes when trying to capture treatment effectiveness (Booth et al., 1997) or routine clinical outcomes (Möller, Demyttenaere, Sacchetti, Rush, & Montgomery, 2003). The same logic has been argued for the definition of remission (Zimmerman et al., 2006, Zimmerman et al., 2006, Zimmerman et al., 2006) since both symptoms and functioning indicate a depressive episode.

The depression literature provides various estimates relating depressive symptoms and functioning. Most researchers examining the relationship use adjectives (e.g., strong, weak, etc.) rather than provide exact correlations. To address this shortcoming, we present a literature review relating depressive symptoms and functional outcomes.

We chose to study depression because depression is one of the three most prevalent and burdensome psychological disorders that affects us all in some way. Latest US estimates show that depressive disorders affect approximately 16% of the population (lifetime prevalence) (Kessler et al., 1994, Kessler et al., 2003) and leads to considerable personal, social and economic loss. Cross-sectionally, survey evidence (Kessler et al., 2003) suggests that roughly 60% of depressed people reported substantial (i.e., severe or very severe) impairment. Furthermore, roughly half (51.6%) received depression treatment but only 2 out of 5 patients (41.9%) responded—only 20% of depressed respondents were successfully treated—and most indicated substantial daily life functional impairment even after treatment. Thus, following treatment, many people continue to live with fewer depressive symptoms that adversely affect functioning. Functional impairment affects not only the depressed person but families, friends, and general society as well. A recent US estimate of depression's economic burden indicates direct costs (diagnosis and treatment) of $2.1 billion and indirect costs (impact on occupational, long-term disability, premature mortality, etc.) of $4.2 billion (Jones and Cockrum, 2000, Baldwin, 2001); cost estimates that rank depression as one of the most costly US health care problems (Wells et al., 1989). The high prevalence, direct impact, and serious society implications gave us the best case scenario for relating symptoms and impairment.

To support prior research initiatives and to provide a deeper understanding of the relationship between symptoms and functioning, we aimed to 1) review the research relating symptoms and functioning, 2) provide a rationale for measuring both outcomes, and 3) discuss potential measurement artifacts. We reviewed the literature to summarize and examine the relationship between symptoms and functioning.

Reviews of social (e.g., social alienation (Coyne and Downey, 1991, Joiner and Katz, 1999, Joiner, 2000, Coyne et al., 2002), marital discord (Coyne et al., 2002), and social interactions (Coyne, 1976, Segrin and Abramson, 1994, Nezlek et al., 2000, Wildes et al., 2002, Petty et al., 2004)), behavioral (e.g., physical activity (Allgöwer, Wardle, & Steptoe, 2001), engagement in pleasant activities (Lewinsohn & Graf, 1973), and engagement in high risk activities (Allögwer et al., 2001)), biological (e.g., adrenergic system changes (Dubini, Bosc, & Polin, 1997) and prefrontal cortex activity (Fu et al., 2001, Davidson et al., 2002, Stone et al., 2007)), and economic (Chisholm, Sanderson, Ayuso-Mateos, & Saxena, 2004) indicators of depression converge on the same conclusion—depression adversely affects human functioning. These reviews, however, contain no specific information about the magnitude of the relationship. Regardless, depression experts hold that the relationship exists and most consider it to be common knowledge today. Mental health experts, for example, acknowledge the relationship in both diagnostics (American Psychiatric Association, 1994) and treatment planning (Kramer, Smith, & Maruish, 2004). We have all come to accept that depression interferes with daily independent living and leads to great suffering for patient, family, and society; the relationship strength, however, remains unclear.

While most researchers and clinicians recognize these implications, severity of depression is almost solely expressed by phenomenological (i.e., symptoms) assessments that fail to address the effects of depression. Furthermore, major depression episodes require functional impairment or distress in “social, occupational, or other important area[s] of functioning” (American Psychiatric Association, 1994). Researchers and clinicians devote considerable resources to understanding and treating depression; measuring both functional and symptom outcomes may only serve to help those efforts. Our intentions are to demonstrate that symptoms and functioning hold a tenuous relationship requiring both to be measured routinely.

Section snippets

Methods

We conducted several comprehensive literature searches of PubMed, Cochran Collaboration Archives, PSYCInfo, Google, and relevant article reference lists. There was no time constraint used for the search; we used all articles meeting our search terms on June 30th, 2007. The first search focused on identifying symptom and functional outcome measures used in depression research. Our aim was to identify every relevant general and domain-specific measure used with depressed samples. An initial

The association between depressive symptoms and global functioning

Many functional outcomes relate to depressive symptomatology; global functioning serves as the best starting point. Most of the work directly relating depressive symptoms to global functioning focuses on mean differences. These mean differences, however, do not convey the relationship between the two outcomes. Some research, however, offers correlations (e.g., Shelton et al., 2001).2

Discussion

The current study is the first study to review and document the relationship between depressive symptoms and functional outcomes. We found that administration time had a statistically significant prediction of those correlations, however, we interpret these results with caution. Correlations present many methodological complications and likely result in weak inferences. Nevertheless, the overall modest correlations may be indicative of two things: 1) depressive symptom and functional outcome

Conclusion

We focused on correlations between depressive symptom and functional outcome measures. While the results indicated a moderate correlation, other non-correlational work (e.g., Hays, Wells, Sherbourne, Rogers, & Spritzer, 1995) shows the impact of depression is equal to or worse than the impact of other chronic medical conditions (e.g., diabetes, hypertension, heart attack, and congestive heart failure) on general functional impairment. This review stepped through three specific aims to

Acknowledgement

Patrick E. McKnight was supported by the National Institute of Arthritis, Musculoskeletal, and Skin Diseases R01-AR-047595. Todd B. Kashdan was supported by National Institute of Mental Health grant MH-73937.

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