This meta-analysis found that psychotherapy administered over the telephone was associated with significant reductions in depressive symptoms. The comparison of telephone-administered psychotherapy with control conditions, while meeting statistical criteria for significance, found a mean effect size of d
= 0.26, which is somewhat less than the d
= 0.42 reported in a meta-analysis that compared face-to-face psychotherapy to no-treatment controls (Wampold et al., 1997
). However, the pre–post finding of d
= 0.82 for telephone-administered psychotherapy is in line with many findings of meta-analyses of pre–post outcomes for face-to-face therapies in the d
= 0.71–0.73 range (Nietzel, Russell, Hemmings, & Gretter, 1987
; Robinson, Berman, & Neimeyer, 1990
). Part of this discrepancy may be due to the control conditions used. Many of the control conditions used in studies included in this meta-analysis provided patients with active treatment conditions. For example, patients in the TAU condition in Simon's and Tutty's studies (Simon et al., 2004
; Tutty et al., 2000
) were under the care of primary-care physicians who prescribed antidepressant medications. Most of the remaining studies were conducted with patients who had some form of severe medical condition (e.g., multiple sclerosis, lung cancer, breast cancer, AIDS), which put them in frequent contact with medical care providers who may or may not have prescribed medications (Bailey et al., 2004
; Heckman et al., 2006
; Mohr et al., 2000
; Napolitano et al., 2002
; Sandgren & McCaul, 2003
). In contrast, many psychotherapy studies using no-treatment conditions prohibit any psychological or pharmacological intervention outside the study and/or do not include patients with medical conditions that bring them into frequent contact with physicians who could potentially identify and treat the depression.
The mean attrition rate was 7.6% across all the studies. A meta-analysis of 125 studies reporting dropout from face-to-face psychotherapy found a mean attrition rate of 46.9% (Wierzbicki & Pekarik, 1993
). This figure may be somewhat higher than is found in clinical trials, as it included a broad range of studies. A review of 14 major clinical trials, including psychotherapy for depression, over the past 20 years found attrition rates ranging from 13.9% to 64.4% (Blackburn & Moore, 1997
; DeRubeis et al., 2005
; Elkin et al., 1989
; Gallagher-Thompson & Steffen, 1994
; Hollon et al., 1992
; Keller et al., 2000
; Miranda et al., 2003
; Scott & Freeman, 1992
; Shapiro et al., 1994
; Thompson, Gallagher, & Breckenridge, 1987
; Ward et al., 2000
; Watson, Gordon, Stermac, Kalogerakos, & Steckley 2003
; Williams et al., 2000
). These attrition rates fall outside the 95% CI for attrition from telephone-administered psychotherapy reported in this review. Therefore, these findings support recent observations that telephone administration of psychotherapy may reduce attrition by overcoming barriers to care (Mohr et al., 2005
; Simon et al., 2004
). However, as with the efficacy findings, due to differences in samples used in telephone-administered and face-to-face administered psychotherapy studies, it is premature to draw any firm conclusions regarding the relative attrition rates between telephone-administered and face-to-face administered psychotherapies.
There was significant heterogeneity across the studies for both the pre–post treatment and attrition analyses. Secondary analyses suggested that some of this variability could be accounted for by therapist specialization and that attrition may be higher in group treatments. In addition, cognitive–behavioral treatments had higher attrition rates, although this may have been driven by the group treatments. The secondary analyses accounting for unexplained variance are based on small numbers of analyses and are at best suggestive.
There are several other potential explanations for the heterogeneity in outcomes, including variability in baseline severity of depressive symptoms and the wide variety of comorbid illnesses across studies. Unfortunately, these could not be controlled for. The variety of measures for depressive symptoms used made it difficult to reliably rank the baseline depressive symptom scores on severity, thereby eliminating the possibility of covarying the effect of severity. Likewise, the populations from which telephone-administered psychotherapy study samples are drawn include a wide variety of primarily medical populations with barriers to treatment. Unfortunately, due to the degree of heterogeneity in comorbidities (seven studies focused on five different specific severe illnesses, one study identified a variety of chronic illnesses, three studies focused on medical practices with unspecified medical comorbidities, and one study targeted chronic depression), it was not possible to account for these comorbidities statistically.
A potential limitation in the study is that the variability in medical comorbidities may have contributed to the heterogeneity in outcomes in at least two ways. First, the various medical illnesses may have had variable effects on depressive symptoms and/or may have had a moderating effect on the efficacy of psychotherapy. Prevalence of depression in some of these illnesses exceeds prevalence in the general population, and it is possible that some depressive symptoms may result from the pathology or pathogenic processes of the medical disorders (Feinstein et al., 2004
; Mohr & Cox, 2001
; Then Bergh, Kumpfel, Trenkwalder, Rupprecht, & Holsboer, 1999
). While a growing number of studies indicate that for many medical illnesses, such as cancer, heart disease, HIV, multiple sclerosis, and others, face-to-face administered psychotherapies for depression are highly effective (Elliott & Roy-Byrne, 1998
; Lett, Davidson, & Blumenthal, 2005
; Meyer & Mark, 1995
), it remains unclear if these medical illnesses moderate the effects of psychotherapy.
A related potential problem lies in the measurement of depressive symptoms. Many of these illnesses produce symptoms that are confounded with symptoms of depression, such as fatigue and diminished cognitive capacity. However, the comorbid illnesses targeted by the studies included in this meta-analysis are all chronic or have symptoms that continue longer than the treatment periods. Thus, while it is possible that medical illness may elevate depressive symptom scores at any single assessment time point, any decrease in depressive symptoms over time is most likely due to changes in depressive symptoms and not to the more chronic medical symptoms.
We also want to emphasize that it is premature to generalize the results of this meta-analysis broadly. Individual studies suggest specific uses under specific circumstances; for example, telephone therapies may provide added benefit compared to care for depressive symptoms by a primary-care physician or to no care at all. However, because the depression symptom outcomes used in this meta-analysis were self-report instruments, the generalizability of these findings to clinically diagnosable depressive disorders is limited (Kendall & Flannery-Schroeder, 1995
). Furthermore, the measures of depression used in this study had a wide range of specificity and sensitivity (Minami, Wampold, Serlin, Kircher, & Brown, 2007
). Thus, the aggregated effect size estimates for depressive symptom severity should not be used as any sort of benchmark. In addition, the level of heterogeneity across studies suggests that we do not yet understand the characteristics of patients for whom such telephone interventions may be effective, and those for whom telephone intervention may not be appropriate. The heterogeneity in the severity of depressive symptoms and in medical comorbidities in the samples also limits generalizability.
Another important limitation of the study is that attrition was not defined with any specificity beyond having dropped out at any point during the study. This was due to the fact that trial reports typically do not distinguish attrition early in treatment from attrition later in treatment. This may mask important differences in the effect that attrition at different stages of treatment may have on outcomes. For example, failure to initiate treatment after randomization, or dropout in the initial three to four weeks of treatment (failure to engage), likely has very different ramifications compared with patients who remain in treatment for many weeks, but fail to complete the total number of sessions as specified in the protocol. It would be useful if reports of clinical trials differentiated among these different forms of attrition.
Thus, the most appropriate conclusion of this meta-analysis is that delivery of psychotherapy for depressive symptoms is promising but requires more research. A few questions critical to our ability to make broader clinical recommendations remain unanswered. Most centrally, it is not clear whether telephone-administered psychotherapy is equivalent to face-to-face administered psychotherapy in reducing depression and whether telephone-administered psychotherapy can produce lower attrition rates, compared with equivalent face-to-face treatments. These conclusions can only be drawn from randomized trials directly comparing face-to-face and telephone-administered treatments. Telephone administration of psychotherapies may also have deleterious effects. It will be important to begin identifying specific populations for whom such treatments are useful, and perhaps more importantly, populations for whom telephone-administered psychotherapy is contraindicated. Trials addressing these questions are urgently needed, as organizations that provide mental health care have already begun implementing telemental health programs (Maheu et al., 2005