The aim of our study was to analyse whether psychopathology as assessed by the AMDP-system at admission to psychiatric hospital as well as other variables (e.g. treatment assessed at the end of hospital stay) are suitable to predict LOS. The study was conducted in the context of the current discussion on new financing systems in Swiss psychiatry in order to gain knowledge bearing on future expenditure.
We examined eight multivariate statistical models. Psychiatric syndromes (models 1 and 2) or psychopathological symptoms (models 3 and 4) explained about 5% of the variation of LOS. The consideration of syndromes or symptoms and further characteristics (models 5-8) led to an explained variation of about 25%, with a weak association between AMDP-psychopathology and LOS. Apathy (model 5) or the depressive syndrome (model 6) were the only syndromes that remained in final statistical models. Further, symptoms that were included in model 7 or model 8 referred to the apathetic or depressive syndrome. Specific admission for crisis intervention explained about 15% of variation in LOS.
Our results enhance previous findings on the predictive power of syndromes with a smaller sample [20
], as here psychopathological symptoms also do not allow sufficient prediction of LOS. Other clinical variables besides psychopathology such as substance abuse or severity of illness at admission had a minor influence on the length of stay as well, which is in line with previous findings taking several hospitals in a whole catchment area into account while controlling for the factor "hospital" [11
]. According to a previous study [21
], the consideration of variables related to treatment within hospital stay led to an explained variation of more than 20%.
One reason for the poor association between psychopathology at admission and the LOS could be attributable to its inherent characteristics. On the one hand, descriptive and dimensional measures of psychopathology might indeed better represent the patient's current mental condition than diagnosis as outlined in the introduction. However, the changeability of psychopathology implies that it could be affected by factors within and beyond inpatient treatment, which might influence LOS. Accordingly, changes in clinical condition might be better related to LOS than severity of illness at hospital admission. An earlier study reported that grouping patients on the basis of severity ratings that take the treatment process into account (e.g. symptoms from admission to discharge, level of care, response to therapy, acute symptoms at discharge) led to an explained variation of the LOS of up to 50% [26
]. Regarding clinical practice, imagining a severely manic and/or psychotic patient with high psychopathological scores who is rapidly remitting under adequate medication and discharged after 10 days, also because he or she desires this, would be an example of high scores on psychopathology and a short stay. On the other hand a schizophrenic patient with low acute psychopathology but with a disturbed social network outside, for instance regarding appropriate accommodation, might long remain in hospital until the necessary subsequent support is initiated. Another example would be a patient with an acute but rapidly remitting depressive crisis versus a patient with a depressive personality and a complicated course of illness including social problems.
We further considered treatment-related variables within hospital stay or compulsory medication which were assessed at hospital discharge. However, usually physicians determine an appropriate treatment strategy right at the beginning of a patient's hospital stay, which could be adjusted over time in hospital. Obviously LOS is more strongly related to a specific global treatment approach (in this study crisis intervention or acute care) characterised by its duration compared to clinical measures, whenever these are less well-defined categorisations susceptible to subjective estimations. There might be further clinical or social factors associated with the patient's medical condition. This could refer to etiological features of the mental disorder as heredity, childhood or other trauma or psychosocial burden. Little is known about the relationship between psychosocial needs [27
], chronicity of the mental illness or response to previous treatment [27
] and the LOS. The variable social support has been considered as an important predictor of LOS in previous studies [28
Further, there might be factors unrelated to the patient which influence LOS. For example, studies including organisational variables (e.g. number of staff, ward, type of hospital) show an explained variation of more than 20% [21
]. The inclusion of variables referring to the care system (e.g. number of staff, contact rate in outpatient care, sociodemographic structure) also led to an explained variation of 20% [29
]. It is not clear how much of the variation in LOS is due to factors like treatment philosophy of a hospital or the physician in question or further structural variables (e.g. waiting time before referral to another institution, quality of outpatient care). However, such "external" factors are not related to individual treatment needs. Nevertheless, the findings mentioned give important hints as to factors that influence LOS. Such results on predictors might facilitate the physician's appropriate assessment of LOS [6
Our results might have implications for future research on LOS and payment in inpatient psychiatry. First, it might be worthwhile to focus on patients with higher apathy or depressive syndrome. There seems to be a need for investigating (or developing) clinical measures that are more strongly related to clinical practice. The consideration of more detailed information on treatment in routine assessment could be promising. With respect to financing, our findings suggest that psychopathology at admission is not suitable to serve as a basis for estimating resource use. Another question is whether resource use could be sufficiently predicted at all. Some alternative models to prospective costing are currently examined. One example is the development of a budgeting system on a day to day basis which takes patient-characteristics and treatment into account [12
]. At present, the Canton of Zurich is investigating whether mixed financing (combining daily rates and case-based remuneration) might be effective in reducing LOS and in preventing early readmissions [12
We have to consider some limitations. The included sample contained relatively less patients from the psycho-geriatric wards than the excluded sample but a slightly higher proportion of patients with an affective or psychotic disorder, whenever the proportion of diagnoses between both samples was still of a comparable magnitude. We consider this limitation to be a minor one, because the assessed question on psychopathology and LOS presumably does not depend on such small differences concerning case mix, all the more as LOS and diagnosis are not strongly related [11
]. Such, our results are to be regarded as valid for a case mix as can be found in general psychiatric hospitals with adult psychiatric patients. Further, data on validity or reliability of the clinical ratings are not available. However, physicians did receive special training in performing these ratings and they were performed as well as possible in the routine clinical setting. We used LOS as a proxy for resource consumption but LOS is only one of several factors (e.g. amount of service provision per day) that lead to costs. Our approach to assessing treatment variables was on a relatively unspecific level and should be made more specific if intended for assessing resource consumption. Finally, AMDP-data are here only related to one specific hospital (and one specific catchment area) in the whole Canton of Zurich. To validate our findings, it might be considered performing such investigations in other countries or in different healthcare systems.