The average age of our study sample was 44 years and the Global Severity Index was one (out of four), i.e., patients who were clinically stable, without residual symptoms, with good social and family adjustment, autonomous or with minimal dependency and in regular contact with services. The average number of outpatient contacts per year was 11.14. Despite this global severity index, only 18% were working. In Spain, as in other European countries, this employment status is common in persons with schizophrenia, with rates ranging between 10% and 20% [30, 31].
This study used a linear regression approach to examine different factors (such as the socio-demographic and clinical characteristics of the patients and their use of services) possibly related with the use of community mental health services. This multilevel analysis in which adjustment was made for possible effects of clustering explained nearly 50% (46.35%) of the variance in contacts with the outpatient mental health services. In the field of public health this approach is considered a very good explicative model.
After controlling for socio-demographic, clinical, professional and service use variables, no gender differences were found concerning the use of outpatient services, similar to the results of Lindamer et al. . Unlike some reports [8, 9], our findings suggest that age is not associated with the number of outpatient contacts, though this may be related to under-representation of elderly patients. Variables concerning type or place of residence showed slight significance (p < 0.05).
After adjustment, the number of outpatient contacts was positively associated with no formal education and not working, receiving welfare benefits. It is well known that patients receiving welfare benefits are heavy users of outpatient mental health services . The first reason for this is that the illness of these persons is more severe than those who are working. Another reason could be that welfare benefits need to be revised routinely according to information supplied by the psychiatrist. Yet another reason concerns the fact that persons who do not work have more free time to attend health services. The level of education can also play a role, and our results show that a lower educational attainment increases the risk of higher service use. This could be due to less tolerance or knowledge of the illness and to an increased need to seek help. Nevertheless, our results concerning level of education differ from those found by Pezzimenti et al.  and Cooper-Patrick et al. , where a high level of education was associated with greater use of ambulatory services.
As expected, an increase in the level of severity was generally associated with a greater frequency of outpatient contacts [8, 33]. This group of patients presents frequent decompensation, moderate disability and predominantly negative symptoms. But what is important to highlight, concerning the efficiency of the attention, is that the group with the highest severity level (level IV: higher disability, without support and with serious symptoms), showed a weaker association with frequency of use (p = 0.06), probably due to lower adherence to treatment in this group. The strong relationship between having inpatient admissions and a higher number of outpatient contacts implies that patients who had been in hospital were receiving continuity of care because of decompensation of the illness, reflected in a higher number of contacts with community services. This result is similar to the findings by Kent et al.  and Roick et al. , which showed that frequent users of psychiatric inpatient care also consume more outpatient services. The particular psychiatrist attending a patient was strongly associated with the total number of outpatient contacts. As the type of patient was similar for all the psychiatrists, this result could be a consequence of differences in the characteristics of each professional related, for example, to his or her length of clinical experience, professional orientation, the case load size or burnout. Some studies have suggested that psychiatrists have higher levels of burnout than other physicians employed in general medical settings [36–38]. This finding, called "induced demand by the professional", is well known in the field of health services and in health economics , but as far as we know, no study in the psychiatric area has focused on patients with schizophrenia and analyzed the effect of the attending psychiatrist as a possible factor related with differences in outpatient contacts. Finally, the strongest association was with the type of professional seeing the patient. The patients who had contacts with both types of professional, nurses and psychiatrists, had significantly more contacts with the community centre than the patients who only had contacts with psychiatrists. A possible explanation for this concerns the profile of patients receiving combined treatment (both psychiatric and nursing), who usually have a low functioning level and more problems in basic everyday living skills, with more chronic and negative symptoms . Nurses play a relevant role in the care of patients with schizophrenia, centred mainly on achieving maximum patient autonomy and adaptation to the social environment through control of antipsychotic medication or with psychosocial interventions . In addition, many nurses visited their clients at their place of residence. Some studies have shown that the structure of the service delivery system  and staff can be major determinants of heavy psychiatric service use , though this has mainly been studied in hospital settings . Lemming and Calsyn  showed that social support from professionals was the strongest predictor for service utilization in persons with severe mental illness.
Strengths and limitations of the study
This study has several strong points. The analyses are based on a large sample of data extracted from a Mental Health Information System (RESMA). The homogeneity of the study population (users with schizophrenia or related disorders living in the community) provides a non-biased picture of the overall use of clinical services, and not just for patients with previous hospitalization, as seen in most studies. Another strong point is that the study includes an operationalized definition of the use of services, defined as the number of contacts with outpatient mental health services, which we calculated after excluding the number of days each patient had been hospitalized in a psychiatric ward. This provides more realistic information about use of services. Furthermore, we used multilevel linear regression with two levels, patients and primary care centres.
However, before accepting the validity of our results, it is important to consider some limitations. First, and perhaps most importantly, this was a cross-sectional study. Accordingly, we cannot infer causality but only association between factors and our dependent variable. Secondly, the diagnoses were clinical (no structured interviews were used) and the validity of the Global Level of Severity is unknown. However, these assessments were done by specialized psychiatrists who care for patients over a long time  and for the GLS we calculated test-retest agreement at two times, with a good coefficient according to Streiner . Third, as the sources of data in this study were routine clinical databases, reliability of data completion in the clinical practice cannot be assured given the difficulties this task sometimes involves in this setting. However, concerning this matter, we used an imputation method to compensate for the missing data. Finally, as data were recorded in the public service setting, care provided by private psychiatrists or psychologists was not included. Nevertheless, in psychotic patients, a progressive shift of patients from the private sector to the public systems occurs as the illness becomes chronic . Thus, we can assume that the sample was representative of the patients with schizophrenia and related disorders in Malaga, always considering a similar Global Level of Severity.