Description of included studies
All inclusion criteria for studies on psychological treatment in primary care were met by 15 studies, in which 20 psychological treatment conditions were compared to a control group.15–21, 34–41
In these 15 studies, a total of 1505 patients participated (804 in the psychological treatment conditions and 701 in the control conditions). Selected characteristics of the studies included are presented in . A flow chart of the inclusion of studies and the reasons for exclusion are presented in .
Patients in seven studies were referred to the study by the GP, while in six other studies patients were screened for depression (while waiting for their GP, or by a postal questionnaire sent to patients who had recently been seen by their GP). Mixed methods were used in the remaining two studies, or the recruitment method was not clear. Other characteristics of the studies and the comparisons between psychotherapies and control conditions can be found in (diagnosis; type of psychotherapy; number of sessions; type of control group, intention-to-treat analyses, and country where the study was conducted).
Meta-analyses of studies examining effects of psychological treatment of depression in primary care compared to control conditions at post-test: overall results and subgroup analyses.a
The pre-test scores on the BDI were available in eight studies (11 comparisons). In 10 of these 11 comparisons the pre-test BDI scores fell inside the range of moderate to severe depression (BDI between 19 and 29), while the mean BDI score was in the severe range at pre-test in only one of the studies. The pre-test score on the HAM-D was available in seven studies (eight comparisons) and ranged from 13.3 to 22.3 (six comparisons below 20 and two above).
The quality of the studies varied. Blinding of assessors was reported in 13 studies and eight studies reported that allocation to conditions had been conducted by an independent party. Drop-out numbers ranged from 3.3% to 41.2% (one study did not report drop-out). Intention-to-treat analyses were conducted in 10 studies and all patients who were randomised were used in these analyses, whether or not they dropped out of the intervention or study; the other studies were limited to completers-only analyses.
Psychological treatment in primary care versus control at post-test
The overall mean effect size of psychological treatment versus the control conditions at post-test was 0.31 (95% CI = 0.17 to 0.45), which is usually considered to be a small effect.30
Heterogeneity was significant (Q = 34.91; P
<0.05), but low to moderate (I2
= 45.58). The NNT which corresponds to an effect size of 0.31 was 5.75. Details of these results are shown in and .
Standardised effect sizes of psychological treatment of depression in primary care patients compared to control conditions at post-test (A and B indicate two treatments from one study that were compared to a control group).
The analyses included studies in which more than two psychological treatments were compared to a control group, which means that multiple comparisons from one study were included in the same analysis. These multiple comparisons are not independent of each other, which may have resulted in an artificial reduction of heterogeneity and a bias in the overall mean effect size. Additional analyses were conducted as a consequence, in which only one comparison per study was included (). Only the comparison with the largest effect size was included first, followed by another analysis including only the smallest effect size. shows that the results did not differ very much from those in which all comparisons were included.
Comparable effect sizes were found (d = 0.43; 95% CI = 0.22 to 0.64; Q = 26.30, not significant;I2 = 50.57; n = 14) when the analyses were limited to the effect sizes found for the BDI. The result was the same when the analyses were limited to the effect sizes found for the HAM-D, which is a clinical interview (d = 0.49; 95% CI = 0.30 to 0.68; n = 7); however, heterogeneity was zero in these analyses (Q = 5.34; not significant; I2 = 0).
Neither the funnel plots nor Duval and Tweedie's trim and fill procedure indicated a significant publication bias. The effect size decreased somewhat after adjustment for possible publication bias (adjusted effect size: d = 0.20; 95% CI = 0.05 to 0.34), but the observed and adjusted effect size did not differ significantly.
The effects of psychological treatments at follow-up were not examined. No effect sizes were available at follow-up in nine studies (either because no follow-up assessment took place, or because a waiting list control group was used and this control group had received treatment at follow-up). The attrition rate was higher than 50% in one of the remaining six studies,39
while the follow-up periods ranged from 3 to 36 months in the other five studies. Because of the small number of studies and the large differences in follow-up periods, the results of the treatments at follow-up were not pooled.
Several subgroup analyses were conducted, using the characteristics of the studies as described in the above section on ‘Data extraction’, except that subgroup analyses were not conducted with the target population, because all studies focused on adults in general. In addition, recruitment method (community recruitment, recruitment from clinical samples, and other recruitment methods) was not examined in these subgroup analyses, because patients in all these studies were recruited through primary care. The results of the subgroup analyses are presented in .
The studies in which patients were recruited through systematic screening resulted in a significantly lower effect size (d = 0.13; 95% CI = –0.08 to 0.34; Q = 9.82, not significant; I2 = 38.89) than studies in which patients were referred directly by the GP (d = 0.43; 95% CI = 0.28 to 0.58; Q = 9.71, not significant; I2 = 0). The effect size for the studies in which patients were recruited through systematic screening was not significantly different from zero. There was a significant association (P <0.05) between effect size and the country where the study was conducted. Studies in the UK found a higher mean effect size (d = 0.45; 95% CI = 0.28 to 0.62) than studies in the US (d = 0.11; 95% CI = –0.15 to 0.38) and the two studies in the Netherlands (d = 0.10; 95% CI = –0.15 to 0.35); heterogeneity was low to moderate in the three subgroups, and the results of the studies in the US and the Netherlands were not significantly different from zero. There was a trend (P<0.1) indicating that studies using intention-to-treat analyses resulted in lower effect sizes (d = 0.23; 95% CI = 0.05 to 0.42) than studies using completers-only analyses (d = 0.47; 95% CI = 0.27 to 0.68).
Most BDI and HAM-D scores at pre-test were in the same range of severity (moderate to severe), which meant it was not possible to examine whether severity at pre-test was related to the effect size.
Psychological treatment in primary care versus other settings
The effect sizes found for psychological treatments in primary care were relatively small compared to the results of psychological treatments for depression in general42,43
and, therefore, treatments delivered in primary care were compared directly with these treatments when conducted in other settings (such as in samples recruited through media announcements, or in clinical samples from specialised mental health care). A literature search identified 99 studies in which psychological treatments in other outpatient settings than primary care were compared to a control condition. These 99 studies included a total of 154 comparisons between a psychological treatment and a control group; 6427 patients with depression participated in these studies: 3843 in the experimental groups and 2584 in the control groups. Patients in 55 of the 99 studies (55.6%) were recruited from the community; patients in nine studies (9.1%) were recruited from specialised mental health services; patients in 18 (18.2%) studies were recruited through systematic screening (not in primary care, but in community or general medical samples); and 17 studies (17.2%) used other recruitment methods. Other selected characteristics of the 154 comparisons can be found on the website of this project (www.psychotherapyrcts.org
The effects of the psychological treatments in primary care (d = 0.31; 95% CI = 0.17 to 0.45) were compared with those in other settings (d = 0.67; 95% CI = 0.58 to 0.75), and it was found that this difference was highly significant (P<0.001). Results of these analyses are presented in . Very high effect sizes (d>2.0) were found in some studies (conducted in settings other than primary care) and the possibility that these could be outliers led to another analysis from which these potential outliers were excluded. The difference between studies in primary care and those in other settings remained highly significant (P<0.001) in these analyses. This difference was also highly significant when only one effect size per study was used and when the analyses were limited to effect sizes based on the HAM-D and the BDI ().
A meta-analytic comparison of psychological treatment of depression in primary care and other settings
Multivariate meta-regression analyses
As the significant difference between studies in primary care and those in other settings could have been influenced by characteristics of the populations, the interventions, and the design of the studies, multivariate meta-regression analyses were conducted which controlled for these variables.
For the purposes of the first meta-regression analysis (with the effect size as the dependent variable), all characteristics described in the above ‘Data extraction’ section were entered as predictors, after transforming them into dummy variables. Recruitment through primary care was one of the predictors in these analyses, the results of which are presented in , and it is clear that recruitment in primary care was a significant predictor of the effect size, even after controlling for all other characteristics of the studies (B = −0.41; standard error [SE] = 0.19; P = 0.03).
Regression coefficients of study characteristics in relation to the effect size of psychological interventions for depression: multivariate meta-regression analyses with recruitment in primary care as predictor.
Indications that there were two types of recruitment in primary care resulted in the same meta-regression analysis being conducted once more (with the same predictors), but this time two separate dummy variables were entered for recruitment in primary care: the first one indicated referral by the GP to the treatment, and the second one indicated systematic screening of primary care patients. Results of these analyses are presented in and show that referral by the GP was not a significant predictor (P = 0.38), but systematic screening was (B = −0.60; SE = 0.23; P = 0.01).