We found a relationship between the psychoeducational group intervention and remission of depressive symptoms. More patients from the IG had remission of their depressive symptoms at short and long term compare with the control group. The psychoeducational group intervention proved to be effective in the short term, showing a reduction in the BDI score of 5 points and this symptomatic improvement in the BDI continued to follow up at 9 months. In contrast, the control group needed 9 months to achieve a 3 point improvement in the BDI. We could say that it is an effective intervention in the short term, although the effect size is small.
When analyzing what kind of population can benefit most from receiving the group intervention; mild or moderate depression participants, we found that patients with mild symptoms obtained a higher rate of symptom remission in the short and long term and symptomatic improvement in the BDI remained over the long term, as distinct from the moderate depression group, where the improvement was only significant post-intervention (short term).
Comparison with other studies
Psychoeducation has proved effective as psychotherapy for depressive-symptom management in the Primary Care setting [24, 26–28, 30, 52, 53]. However, there is a need to clarify both the magnitude of the effect (from 0.21 to 0.80) of this intervention and the associated factors that influence the measurement of efficacy. Some factors to take into account have been described: the type of psychoeducational intervention used [24, 26, 27, 29, 30, 53], the clinical rating scale [24, 26, 27, 30, 53], intensity of clinical depressive symptoms at the beginning [26, 28, 54], and the duration of the therapeutic effect of the intervention [24, 26–28, 30, 52].
One of the greatest difficulties in reviewing studies on the effectiveness of group psychoeducation in depression in primary care is that there is no consensus on the definition of psychoeducation. The studies which have used the term "psychoeducation" to define the type of psychological therapy have defined it as an applied educational-behavioral intervention , or interventions with behavioral components (behavior change, pleasant activities), cognition (cognitive restructuring, counseling), education (direct instruction, lectures) and competence (broad skill training) [26, 55]. Thus, we find interventions of various orientations that share a high didactic and psychoeducational group structure. This would include CBT orientation interventions with a psychoeducational group format structure , specific psychoeducational interventions to improve adherence to drug treatment , and multicomponent interventions (stepped care) structured in a psychoeducational group format ; or the CWD course of cognitive-behavioral orientation [14, 24, 26, 27, 31]. Most studies [24, 27, 28, 30, 52, 53] that have used a psychoeducational intervention also included homework for the patient.
In our study, we developed a psychoeducational group intervention protocol that included material from the 12 sessions , a CD with the material from each session and homework for the patient; so reaffirming the concept of psychoeducation in our intervention.
There are few randomized studies of group psychoeducation based on this approach of providing education about the disorder and healthy lifestyle behaviors; aspects that have been shown to help in the recovery of these patients [15, 39, 56].
Most studies that have evaluated the effectiveness of psychoeducation have used the Beck Depression Inventory (BDI) [24, 26, 27, 52, 53] as a clinical assessment scale, which, unlike the Hamilton Rating Scale for Depression (HRSD) , includes the psychological and psychosocial aspects, emphasizing the cognitive component of depression which is a very important issue in primary care.
The effectiveness of psychoeducation in the short term (post-intervention or 3 months) has already been demonstrated [26, 30, 52] and there are no discrepancies between studies. However, with respect to the duration of the therapeutic effect of psychoeducation at 6 and 12 month follow-up, results are controversial. The study by Allart-van Dam  evaluated the long-term preventive effects of an effective CWD course in the same sample of patients as in the earlier study  with a significant effect at 6 and 12 month follow-up (p=0.003 and p=0.03 respectively) but only in the participants with low initial symptomatology (BDI between 10 and 25). The study by Dalgard  evaluated the effect of a modified CWD course on unipolar depression at 6 and 12 month follow-up. Results showed that there was a significant improvement in symptoms (p=0.009) and the effect size at 6 month follow-up was small (d’=.47) but at 12 month follow-up, the BDI in the intervention group remained stable with a difference of 8 points. The study by Dowrick  evaluated the psychoeducation group for depressed adults and the results show us that the psychoeducation intervention reduced the severity and duration of depressive disorder after 6 months, but not at 12 months. In the study by Brown , patients significantly improved their BDI at 6 and 12 month follow-up, and in the study by Araya , significant improvements of 9 points between groups (p <0.0001) were maintained at 6 month follow-up.
Our results shows a significant improvement in symptoms post-intervention (p = 0.029; d’=.29) although the effect size is small but this improvement is not maintained at 9 month follow up (p = 0.24; d’=.16).
If we focus on the severity of initial clinical depressive symptoms, most studies included a sample of patients with an average BDI of 22. When we tried to identify the subgroup of patients which most benefits from this intervention, we divided the population according to their initial BDI: "mild" (BDI ≤ 18) or "moderate" (BDI ≥ 19). It was observed that patients with mild depressive symptoms have significantly improved symptoms in the short and long term (p = 0.001 and p = 0.048, respectively) with a moderate and small effect size (d’=.51 and d’=.44, respectively).
Our results coincide with those found in a review  where it is shown that psychological treatments for minor depression, including psychoeducation, are effective in the short-term (d’ = .42). However, the long-term improvement was not significant. Another study [26, 28] concluded that patients with mild symptoms had low levels of depressive symptoms during the follow-up period, and at one year this population had depression scores that indicated an absence or very low level of symptoms.
However, when analyzing the sample of patients with moderate symptoms, our results show significant improvement in symptoms only in the short-term with a small effect size (d’ = 0.47).
In conclusion, we could say that the effectiveness of psychoeducation would be short-term (post-intervention) in the population with more severe symptomatology while, in patients with mild symptoms, it would be effective at both short and long term (follow-up at 6 and 9 months).
One of the most important aspects of our study is to evaluate the effectiveness of the intervention based on the remission of symptoms.
In relation to the remission of depressive symptoms (BDI ≤ 11) , our results show that 35% of the intervention group (IG) versus 19% in the control group (CG) had depressive symptoms post-intervention, and this 16% difference between groups was significant (p = 0.003). Follow-up at 6 and 9 months showed a significant difference of 14% (p = 0.01), with a 40% improvement in the IG versus 27% in the CG. These data are consistent with those found in one study  which showed that 52.5% of the intervention group did not present depressive symptoms (BDI <10) (Beck, 1988) post-intervention compared with the control group; 31.7%, with a significant difference of 20.8% (p = 0.04) between groups.
When analyzing the sample of patients with mild symptoms (initial BDI ≤ 18), we observed that 57% of the intervention group showed an absence of depressive symptoms versus 31% in the control group post-intervention, with a significant difference between groups of 25% (p = 0.009).
At 6 month follow-up, 59% of the intervention group improved versus 42% of the control group; a difference of 18%, and at 9 month follow-up, 65% improved in the intervention group versus 38% in the control group, with a 27% significant difference between groups (p = 0.006). These results support the effectiveness of this intervention in this subgroup of patients.
When we talk about the remission of symptoms in terms of number needed to treat (NNT), we observed that our NNT of 6.4 post-intervention and 7.4 at 9 month follow-up are supported by those obtained in the study by Dalgard  with a smaller sample of patients (n = 155) which was 6 at 6-month follow-up, and the Dowrick ODIN study  (n = 452) which was 7 at 6 months, supporting the effectiveness of the intervention. Another variable analyzed was quality of life and whether this could be associated with an improvement in depressive symptoms. At first, it was seen that the patients with mild symptoms have better quality of life compared with those with the most severe symptoms, although it has been observed at baseline that milder symptom patients already had better quality of life compared with those with the most severe.
Our results show that psychological intervention improves quality of life for both groups in the short-term, but only the patients with mild symptoms maintain this long-term improvement. No significant differences were found between the intervention group and the control group but this may be due to methodological issues related to the questionnaire used, EQ-5D, which has no cut-off points.
According to the results, this intervention is effective in both the short and long term with high rates of remission in patients with mild depressive symptoms.
We should mention the minor depression has a prevalence of 5–16% in primary care patients  and is an important risk factor for major depression, which develops in 10–25% of patients with subthreshold depression within 1–3 years . It is also associated with psychological suffering, significant decrements in health, impairment in daily living activities and has a considerable impact on quality of life .
Strengths and limitations of this study
Our trial has a number of strengths: firstly, it is the first study to assess the effectiveness of this psychoeducational group intervention which includes health education about the disorder, healthy behaviors, social skills and cognitive-behavioral techniques. Secondly, determining the target population; in this case patients with mild depression. Third, the study was conducted in Spain, specifically in Catalonia, and this is the first multicenter randomized study that assesses the effectiveness of a psychoeducational intervention in this country. Fourth, the sample population was representative of all Barcelona. The PCC participants were located in various areas of Barcelona, with different socio-demographic and economic resources. And finally, highlighting the role of the nurses who led the psycho-educational groups.
Despite the positive findings, potential biases need to be considered when evaluating the study. Some of the limitations of the study could be as follows: firstly, we performed a randomization of patients, but there is no double-blind, the patient knows who belongs to the intervention or control group, as do the nurses and doctors in the PCC. It was difficult for researchers to remain masked to group allocation. However, participants completed self-rating assessments of mood and quality of life. Therefore, that lack of blindness should not have affected our primary outcome to any great extent.
Secondly, the study employed only a two-outcome measure, BDI and EQ-5D, as we wanted the study to be as close as possible to the usual practice of the Primary Care Centers. It is a naturalistic study. Thirdly, the remission of depression was assessed by a screening questionnaire (BDI) rather than a diagnostic interview. Fourth, the overall drop-out was 23%, when we estimated a loss rate up 15%. This loss rate would affect to estimate the real evolution of the BDI a long-term. There wasn’t difference between groups in the loss rate. These losses are consistent with those found in other studies; between 25% and 37% [14, 18]. Finally, further studies are required to confirm these results.