The present analyses sought to examine the rate of sudden gains in IPT for depression. In addition, we sought to identify demographic and diagnostic characteristics that may be associated with sudden gains in IPT, and examined the influence of interpersonal functioning on the occurrence of sudden gains. In accordance with our hypothesis, sudden gains did occur in IPT and occurred at a rate that is consistent with rates reported in other studies. In the present study, sudden gains occurred to 33.5% of the sample. This figure is relatively consistent with data from previous work. Most other sudden gains studies show rates of sudden gains in the high 30% to low 40% range. This work adds to the growing evidence that sudden gains are a robust finding across interventions. It further reinforces the consistent finding that approximately 40% of a given depressed population experiences a sudden and precipitous improvement in symptomotology over time.
Contrary to our hypotheses we found no differences between sudden gainers and other participants in terms of baseline demographic or diagnostic characteristics. Previous work in the sudden gains area (Hardy et al., 2005
; Kelly et al., 2005
; see also Grilo, Masheb & Wilson, 2006
, for similar null findings in CBT for binge eating) has shown inconsistent associations between demographic characteristics and sudden gains such that a clear pattern of association between baseline characteristics and sudden gains has yet to be identified. Further, sudden gainers were no more likely to achieve sustained remission from depression with IPT alone compared to those who did not experience a sudden gain.
Using a measure to determine clinical outcome that is different from the one used to determine sudden gains (i.e.: clinician-rated HRSD versus self-reported BDI) carries the benefit of reducing a potential tautology that occurs when the same measure is used to assess both sudden gains and treatment outcome. Having a sudden gain implies that the participant has enjoyed a substantial improvement in symptomotology at some point during treatment on a given measure. While having a sudden gain is neither necessary nor sufficient to cause remission, if the same measure is used to determine both sudden gains and treatment response, those with sudden gains are, by definition, more likely to remit. Thus our use of two separate measures, the HRSD-17 for outcome and the BDI to define sudden gains, represents a more conservative approach than what has been done in previous research. Nevertheless, we note that a similar pattern of findings emerged when BDI scores were used to predict outcome (see footnotes 2–4
Contrary to hypotheses, those who had sudden gains on the BDI did not achieve remission from depression as defined by HRSD any faster than those who did not have sudden gains. Although researchers in adult depression have not generally conducted survival analyses to examine the relationship between sudden gains and time to remission, Gaynor et al. (2003)
found that adolescents experiencing sudden gains remitted with psychotherapy twice as quickly as those who did not have a sudden gain (5 sessions v. 9.5 sessions). Similarly, while Tang et al. (2000) found that individuals with sudden gains during acute CBT treatment faired better in long-term follow-up, in the present data, patients who had a sudden gain during the course of acute IPT treatment had no apparent advantage during long-term maintenance. It should be noted, however, that relatively few individuals relapsed over the 2 years of maintenance therapy.
Potential explanations for the apparent lack of importance of sudden gains in IPT may be drawn from the differing theoretical rationales and putative mechanisms of IPT and CBT. In theory, CBT works to reduce depressive symptoms by teaching patients the skills required to restructure their thinking patterns so that the world can be viewed in a less pessimistic light. For some CBT patients, acquiring and applying skills in cognitive restructuring and/or making a cognitive shift may be a relatively rapid occurrence, leading to a sudden gain and potentially improving ultimate outcome. In contrast, IPT focuses on changing patterns of interpersonal function, which is likely to be a more gradual and iterative process and less under individual control than cognition. Thus, sudden gains in IPT may reflect a temporary improvement in interpersonal relationships and mood, and have less impact on eventual outcome. Alternately, those who experience sudden gains in IPT may be those whose mood is more reactive to interpersonal interactions, for better or worse. In either case, the experience of a sudden gain in IPT compared to CBT may be prompted by differing causes and may hold quite different clinical implications.
It is especially interesting to note that in previous work, Tang and colleagues (Tang, Luborsky & Andrusyna, 2002
) found that sudden gains occurring during the course of supportive-expressive (SE) therapy, a derivative of psychodynamic therapy that is arguably closer in nature to IPT than is CBT, were less robust and did not predict longer term outcomes as did CBT related sudden gains. These authors suggest that SE therapy-related sudden gains are less robust due to the relative complexity of SE compared to CBT. Similarly, IPT operates by processing emotion and making adjustments to interpersonal interactions rather than using step-by-step methods to adapt cognitions as CBT does. Thus IPT is arguably more complex than CBT and sudden gains occurring in IPT may be more subject to reversal (due to either complexity or interpersonal setbacks) and have limited relationship to ultimate outcomes.
In addition, differential demand characteristics may be at work in these two therapies. In CBT, patients are praised for their ability to minimize negative affect, in both severity and duration, through the skillful use of cognitive restructuring. In IPT, patients are asked to discuss and process affective experiences as they relate to interpersonal interactions more deeply than is done in typical CBT. Thus, while CBT may prompt patients to downplay mood by focusing on cognitions surrounding affective changes, IPT emphasizes mood fluctuations, particularly those that occur in relation to interpersonal stressors. This differing set of therapeutic expectations may promote different patterns of symptom identification and reporting between the two interventions.
To our knowledge, this work represents the first examination of the sudden gains phenomenon in IPT. Further, it is among a minority of studies that examines sudden gains in terms of time to remission. Given that sudden gains and the characteristics associated with them are potentially useful for exploring mechanisms of depression (Tang et al. 1999b
), it is arguably important to consider not only ultimate outcome but also treatment course.
There are, however, several limitations to the current research. First, the sample consisted exclusively of female participants with recurrent depression, limiting generalizability. Patterns and correlates of sudden gains may be different in male or mixed samples and sudden gains may have a differential impact on those with chronic depression or who are in their first episode of depression. Second, although the criteria used to define sudden gains in this study were the same as have been used in previous work (Kelly, Roberts & Ciesla, 2005
; Kelly, Roberts & Bottonari, 2007
), they do differ from Tang and DeRubeis’s (1999)
original criteria. The criteria used here may be slightly more liberal (although rates of sudden gains are similar regardless of criteria) and may be more prone to reversal. Nevertheless, we note that follow-up analyses using the original Tang and DeRubeis’ (1999)
criteria produced a similar set of study results (see Footnote 5
). Last, given that the goal of the parent study was to assess IPT as a maintenance therapy for recurrent depression, medication was made an option to participants who either did not have a 50% reduction in HRSD-17 scores by week 8 with IPT alone or whose symptom profile and symptom severity warranted adjunctive medication. Although individuals were removed from the present sample at the point at which adjunctive antidepressant medication was prescribed, the sample considered here may be representative only of individuals who performed relatively well in IPT monotherapy. Future work examining the impact of sudden gains among patients treated exclusively with IPT over a longer period of time would add to our understanding of the impact of sudden gains on non-cognitive psychotherapies.
In conclusion, the present work indicates that sudden gains do occur in IPT for depression at rates similar to those found in other studies. No clear demographic or diagnostic characteristics were found to be associated with the occurrence of sudden gains. Adding to the mixed results often found in this area of research, IPT-related sudden gains do not appear to provide an advantage to sudden gainers in terms of depressive symptom severity following acute treatment or in time to remission. Sudden gains also did not provide an advantage in terms of durability of remission over time. This suggests potential mechanistic differences between IPT and CBT oriented interventions. Future work examining the pattern and impact of sudden gains in diverse psychotherapies appears to be warranted.