This study incorporated data collected from three different studies using methods that were not identical, although the core set of measures was largely the same. Recruitment methods differed between the South Islington study and the other two, probably resulting in fewer exclusions of severely ill patients in South Islington than elsewhere. Thus the comparison between teams should be treated with considerable caution, even though adjustment has been made for some of the baseline differences that may have resulted from different methods of recruitment. We tested a comprehensive set of variables informed by literature or based on clinical grounds. However, some important variables may have been omitted. Recognised standardised measures were used for ratings of the severity of symptoms and social problems and of risks, but these scales are very broad and global, and more differentiated and sensitive measures of domains such as psychotic symptom severity might have yielded significant associations. The imputation of some missing values (no more than 6% of values for any variable) should be noted. It should also be noted that all findings are associations only: causality cannot necessarily be assumed.
Finally it should be mentioned that this study was carried out in inner city London which represents an area of high deprivation with a transient and cosmopolitan population. The combination of a greater severity of illness and rootlessness means that this population is not typical of the UK as a whole . The high local density of large general hospitals with very busy casualty departments and the high local threshold for admission are each factors which may influence local CRT practices.
Our findings identify factors that may limit CRTs' capacity to treat people at home. They also suggest that some factors expected in theory to limit considerably scope for home treatment may not in fact do so.
One consistent determinant was the particular CRT delivering the service. The difference in recruitment methods discussed above must be noted: even with adjustment for some baseline differences, there may be residual differences, especially between the unselected South Islington sample and the others, that may account for some of the differences found. The areas are socio-demographically fairly similar, but the possibility that differences in catchment area populations or in other aspects of the mental health service system, especially the availability in Islington of crisis houses, may account for differences. The differences found nonetheless raise questions about variations in practice and in admission thresholds between teams, and whether different implementations of the CRT model may produce substantially different results in terms of preventing admission. The content of the CRT model has not been specified in detail, so that it is perhaps best regarded as a service delivery vehicle than as a method of treatment. We need more detailed investigation of the working practices of CRTs and how these influence the effective prevention of admission. A further potentially important factor is the extent to which teams permit patients to choose to go to hospital if this is their preference. Current formulations of the model suggest that home treatment should be delivered whenever feasible and economic pressures certainly favour avoidance of admission, but the increasing emphasis on allowing service users choice conflicts with these imperatives. Participation in a randomised controlled trial may have placed staff under particular pressure to prevent admission wherever possible.
Context of assessment
The location of assessment also influences whether patients are admitted to hospital. Those being assessed in casualty departments were more likely to be admitted after adjustment for all other baseline variables. Possible reasons for this include casualty department time pressures, or the expectation of patients presenting to casualty departments that they will be admitted. Unmeasured differences in symptom severity are another possibility. The casualty department environment may also be one which promotes admission: clinicians are unable to assess patients' home environments and their ability to maintain order there and to cope with daily activities. A more confident appraisal of patients' coping abilities in the community and of their support networks may be possible in patients' homes, encouraging clinicians to opt for home treatment. The environment of the casualty department may also influence patients' behaviour. Our finding regarding casualty department assessments suggests that assessment at home is desirable wherever possible; even following initial attendance to the casualty department. Patients assessed outside usual office hours were also more likely to be admitted to hospital within 8 weeks of the crisis. This might be due to undetected differences in psychopathology, as assessments may take place out of hours because of greater perceived urgency. Lower staffing levels, more junior staff and lack of other resources are other possible explanations.
Patient characteristics and past history
With regards to the characteristics of the patients, the strongest and most consistent finding was that patients who had not been cooperative with the process of arranging the initial assessment were much more likely to be admitted: this association was much stronger than with any clinical variables, suggesting that patients' willingness to engage with services is likely to be the most important single determinant of whether home treatment is feasible. Risk of unintentional self-harm was also a risk factor for admission: self neglect may be more readily manageable with 24-hour staff in hospital than in a home setting. Risk to others also increased risk of admission, reflecting greater caution in managing patients who may be a danger to others or difficulties with home management because of perceived risk to staff. The association between past history of being sectioned under the mental health act and admission suggests that past patterns of crisis management may be difficult to change, although no statistically significant independent association was found between admission in the past 2 years and admission following the crisis.
Comparing our findings with previous studies, there were also some noteworthy negatives. Diagnostic variables did not contribute to likelihood of admission in the final model, and patients with manic presentations, current psychotic symptoms, comorbid substance misuse and personality disorders were all managed at home in substantial numbers. Living alone was also unrelated to risk of admission: while home treatment may be easier for people who have a support network, the impact of introducing a CRT may be greater for a patient who has little other support. Ethnic group also had no clear association with risk of admission when adjustment was made for other variables. Numbers were not large enough to draw any definitive conclusions, but this provides at least some preliminary encouragement that the CRT model may be applicable to people from a range of backgrounds. However, the higher rate of admission for the Black African group, significant on univariate analysis, together with this group's increased risk of compulsory admission, suggests a need to pay particular attention to the needs of this group in future planning of crisis services.
Factors associated with compulsory detention were somewhat different from the others. This was the one outcome not associated with which team treated the patient, suggesting that variations between teams related more to voluntary than compulsory admission. It was also a variable on which ethnic group had a large impact: while in past studies Black Caribbean patients have appeared at greater risk of coercive treatment, we found no evidence of this, but did find an association between Black African group and risk of being compulsorily detained. Which CRT was involved did not influence likelihood of compulsory admission, perhaps not surprisingly given that the Islington studies suggested that overall the impact on admissions was on voluntary rather than compulsorily detained patients [7, 8].
Future service delivery and research
In future research regarding CRTs, greater investigation of the mechanisms underlying these differences in admission rate would be of interest. Analysis of the process of decision making in the early management of crises may enhance understanding of the variations described. Some of the risk factors for admission are potentially amenable to change: for example, avoiding initial assessments in the casualty department might prevent some admissions. A greater understanding is also desirable of patients' views and the factors that make some of them unwilling to cooperate with assessment. In our sample, only a small number of patients were admitted after a week or more of community management, so that there was relatively little scope for examining the characteristics of this group for whom a substantial period of home treatment appears to have failed to prevent admission: focusing on them may be of interest in future investigations. With regard to implications for in-patient wards, this study suggests that the group admitted despite the availability of home treatment is likely to be a relatively challenging one, with high representation of young patients who are unwilling to cooperate with care and pose risks of self neglect or harm to others. In-patient staff is thus likely to require substantial support and training, and good staffing levels in order to manage these groups. The effects on in-patient services of the introduction of intensive home treatment have yet to be examined. Finally, identifying the characteristics of patients who are not successfully managed by home treatment allows consideration of other alternatives to admission that may meet their needs better. For example, residential alternatives to admission, such as crisis houses, may be better placed than CRTs to manage the needs of those who neglect themselves.