Bipolar Disorder
Use of Item Response Theory Methodology to Evaluate Differences Between Bipolar and Unipolar Depression
Lauren M Weinstock, PhD, David Strong, PhD, Lisa A Uebelacker, PhD and Ivan W Miller, PhD
Warren Alpert Medical School of Brown University and Butler Hospital, Providence
Abstract
Despite several decades of research, there remains disagreement as to whether there are unique differences in depression symptom expression between those with bipolar disorder and those with major depressive disorder. Discrepancy across studies may be attributed to many sources, such as heterogeneity across patient samples and research settings, variability in selection of symptoms to be evaluated, and lack of control for underlying depression symptom severity between patient groups. In this article, we briefly review the literature on differential symptom expression between bipolar and unipolar depression, and introduce item response theory (IRT) as one methodology that may be particularly useful in overcoming some of the challenges that have plagued existing research. We review some findings from our research program using an IRT approach to evaluate differences between bipolar and unipolar depression, and conclude with recommendations for future research in this area.
Keywords
Bipolar disorder, major depressive disorder, item response theory, differential item functioning
lauren_weinstock@brown.edu
Affecting approximately eight million people in the US,1
bipolar disorder
and recent data suggest that patients with bipolar disorder will remain symptomatically ill for roughly 50% of their lives.3–5 Consistent with this chronic course, bipolar illness is characterized by marked functional impairment6,7
represents a significant public health concern. Over 90% of individuals diagnosed with the disorder report multiple affective episodes across their lifetime,2
and substantial economic burden.8 Of
particular note, bipolar disorder is potentially fatal. In comparison to the general population, individuals with the disorder are 20 times more likely to attempt suicide, and roughly 15% of patients die from suicide.9 Consistent with this clinical picture, the World Health Organization (WHO) has identified bipolar disorder as one of the top 10 most important public health problems worldwide.10
The Specific Burden of Bipolar Depression
Although the acute impairment associated with mania is indisputable, there is growing consensus that the severe and chronic disability in bipolar disorder may be better accounted for by the depressive, rather than the manic, phase of illness.11–13
Depressive episodes significantly
outnumber manic episodes by a factor of roughly three to one.3–5 Furthermore, depressive episodes are slower to remit than manic episodes,14,15
relapse and recurrence.15
shown that individuals with bipolar disorder spend approximately one- third of their adult lives experiencing depressive symptoms.3–5
© TOUCH BRIEFINGS 2010
and are associated with significantly shorter time to Recent prospective naturalistic studies have
These
data translate into a three- to five-fold greater risk for depressive versus manic symptoms over the course of the illness.
Not only is this pattern of findings evident for bipolar I disorder, it also extends to those with bipolar II disorder. Marked by hypomanic (versus manic) episodes, bipolar II disorder has been typically considered a more mild form of illness. However, research comparing bipolar II with bipolar I disorder has demonstrated that individuals with bipolar II disorder may actually have more frequent and chronic depressive episodes.3,16 Nevertheless, the predominance of depression over the course of bipolar illness is well documented, regardless of disorder subtype.
Diagnostic Challenges in Bipolar Depression
Given the depression-predominant course of illness in bipolar disorder, clinicians often have to rely on retrospective reports of hypomanic or manic episodes to inform diagnostic decisions. It is therefore not surprising that an initial incorrect diagnosis of major depressive disorder (MDD) is most common,17
which may delay appropriate treatment. Even
when unipolar depression is ruled out, it may be difficult to discern between bipolar I and bipolar II disorder when patients present with depressive symptoms. Given this risk for inadequate identification and treatment, it is important to ascertain whether there are unique features of bipolar depression that differentiate it from unipolar depression, and whether there are unique features of depression that may also differentiate between bipolar disorder subtypes. If differences exist,
15
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68