Diagnosis and length of stay at an acute psychiatric unit

While there has been increased research into many aspects of psychiatric admission in Ireland over recent years, relatively little is known about correlates and determinants of length of stay for those admitted. This paper looks in more depth at length of stay following psychiatric admission, with particular focus on the relationship, if any, between diagnosis and length of stay. 

To this end, we studied all admissions (voluntary and involuntary) to an acute psychiatric unit in south west Dublin between January 1, 2014 and June 30, 2015, and compared it with national data. We found that longer length of inpatient psychiatric stay was independently associated with involuntary status and increased age, and was not independently associated with gender, diagnosis, marital status or occupational status. 

Despite these associations, most of the variance in length of stay (92%) remains unexplained by the factors examined in this study, suggesting that other variables, yet to be identified, play significant roles in determining duration of inpatient psychiatric admission.

Introduction

In 2015 there were 17,860 admissions to inpatient psychiatric facilities in Ireland, of which 2,144 were involuntary admissions under the Mental Health Act 2001.¹ While recent years have seen increased research into both voluntary and involuntary admission in Ireland,^2,3 there are still significant gaps in the literature especially in relation to specific topics such as length of stay (duration of admission).

We recently studied patterns of voluntary and involuntary admission in south west Dublin over 18 months in 2014/2015.⁴ We found that rates of involuntary admission had increased in this area compared to previous years but that the overall admission rate was still lower than the national rate. 

We also found that mean length of stay for involuntary patients (59.4 days, standard deviation [SD] 98.0) was substantially longer than that for voluntary patients (18.9 days, SD 38.4; p < 0.001).

The purposes of this paper were to look in more depth at length of stay among all psychiatry inpatients in this area, voluntary and involuntary, with particular focus on the relationship, if any, between diagnosis and length of stay, and to compare with national data published by the Health Research Board, especially in terms of diagnosis.⁵

Methods

We studied all admissions to the acute psychiatric unit in Tallaght Hospital, Dublin (south west Dublin) between January 1, 2014 and June 30, 2015. For each patient, we recorded a range of details including gender, date of birth, marital status, occupational status, date of admission, admission status (voluntary or involuntary for all or part of the admission), date of discharge, and clinical discharge diagnosis using the International Classification of Diseases, Volume 10.⁶

This study was approved by the Joint Research Ethics Committee of St James’s Hospital and Tallaght Hospital and performed in accordance with the Declaration of Helsinki⁷ and Data Protection Guidelines on Research in the Health Sector.⁸

We stored and analysed data using IBM Statistical Package for the Social Sciences (SPSS) Statistics (Version 24). Data were normally distributed except where non-parametric bi-variable tests are specified. For multi-variable analysis, we generated a multi-variable linear regression model with length of stay as the dependent variable. Gender, age, marital status, occupational status, admission status (voluntary or involuntary) and diagnosis were entered as independent variables.

We tested the regression model for multicollinearity, which is when one or more variables are so closely related to each other that the model cannot reliably distinguish the independent effects of each. To test this, we calculated a ‘tolerance value’ for each independent variable; tolerance values below 0.25 indicate possible multicollinearity, and tolerance values below 0.10 indicate significant problems with multicollinearity.⁹

Results

We have already reported that during the 18-month period studied there were 948 admissions of which 13.5% were involuntary.⁴ Over one-third of patients in the study area (39.2%) were discharged within one week and over three quarters (76.1%) were discharged within one month;⁴ these were slightly higher than comparable national figures (29.9% and 67.0% respectively).⁵ The present study focuses more closely on the relationship, if any, between length of stay and various other potentially relevant variables, such as diagnosis, gender, age, marital status and occupational status.

We found that length of stay did not differ between men (median duration of admission: 11 days; inter-quartile range: 3-28) and women (median duration of admission: 9 days; inter-quartile range: 3-24; Mann-Whitney U: 117, 861.5, p = 0.163). Length of stay correlated positively with age (Spearman’s rho: 0.171, p < 0.001) but was unrelated to marital status (independent-samples Kruskal-Wallis test: 1.793, p = 0.774) or occupational status (independent-samples Kruskal-Wallis test: 4.826, p = 0.185). 

Table 1 presents the relationship between diagnosis and length of stay both in the study area and nationally. There are notable similarities between the study area and national data: 58.3% of patients with schizophrenia and 73.1% with affective disorders were discharged within four weeks in the study area, compared to 59.0% and 65.4% nationally.⁵ There are also contrasts: 65.8% of patients with personality disorders and 69.0% with drug disorders (other than alcohol) were discharged within one week in the study area, compared to 49.5% and 51.4% nationally.⁵

On multi-variable linear regression analysis, with length of stay as the dependent variable, longer length of stay was significantly associated with involuntary admission status and older age (see Table 2). We calculated a ‘tolerance value’ for each independent variable in the model and all tolerance values were greater than 0.25 indicating no significant problems with multicollinearity

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Discussion

Longer duration of inpatient psychiatric admission in south west Dublin is independently associated with involuntary status and increased age, and is not independently associated with gender, marital status, occupational status or clinical diagnosis. While it is possible that certain diagnoses are associated with involuntary status, it is nonetheless notable that the collinearity diagnostics in this study indicate that no two variables (e.g. diagnosis and admission status) were so closely related to each other as to render their individual effects indistinguishable from each other.

In terms of strengths and limitations, this study addresses an important issue (length of stay in psychiatric inpatient care); examined a range of variables and co-variates potentially associated with length of stay (gender, age, marital status, occupational status, clinical diagnosis and admission status); used clinical diagnoses coded using the International Classification of Diseases, Volume 10;⁶ and compared results in Dublin south west with national data.⁵

Limitations include the fact that our research is based in a specific suburban area of south west Dublin, which reduces generalisability to other areas. Other limitations include the fact that we did not examine certain variables (eg. country of origin, insight, deprivation), which might well to relate to duration of admission.¹⁰ We also recorded only one diagnosis per patient (when some may have had two or more), and our final multivariable model had low predictive power (8.0%), limiting the conclusions that can be drawn from it. This might be attributable, at least in part, to the fact that we selected the independent variables for inclusion in our model based on both their possible relevance to length of stay and the fact that they were available from existing hospital data sources. Other variables (eg. number of previous admissions, forensic history, etc.) merit future study. 

Conclusion 

Despite the associations between longer duration of inpatient psychiatric stay and both involuntary status and increasing age identified in this study, most of the variance in length of stay (92%) remains unexplained by the factors examined in this study. This suggests that other variables yet to be identified play significant roles in determining duration of inpatient psychiatric admission.

References

1. Daly A, Craig S. Activities of Irish Psychiatric Units and Hospitals 2015. Dublin: Health Research Board, 2016
2. Curley A, Agada E, Emechebe A, Anamdi C, Ng XT, Duffy R, Kelly BD. Exploring and explaining involuntary care: the relationship between psychiatric admission status, gender and other demographic and clinical variables. Int J Law Psychiatry 2016; 47:53-59
3. Ramsay H, Roche E, O’Donoghue B. Five years after implementation: a review of the Irish Mental Health Act 2001. Int J Law Psychiatry 2013; 36:83-91
4. Gilhooley J, Umama-Agada E, Asghar M, McManus S, Whitty PF, Kelly BD. Voluntary and involuntary psychiatric admissions in a suburban area: comparison with national rates, diagnosis and other correlates of involuntary admission status. Ir J  Psychol Med 2017 (Epub ahead of print, 24 August) (https://doi.org/10.1017/ipm.2017.44)
5. Daly A, Walsh D. Activities of Irish Psychiatric Units and Hospitals 2014. Dublin: Health Research Board, 2015
6. World Health Organization. International Classification of Diseases (10th ed.). Geneva: World Health Organisation, 1992
7. World Medical Association. WMA Declaration of Helsinki - Ethical Principles for Medical Research Involving Human Subjects. Ferney-Voltaire: World Medical Association, 2008
8. Data Protection Commissioner. Data Protection Guidelines on Research in the Health Sector. Dublin: Data Protection Commissioner, 2007
9. Katz MH. Multivariable analysis. Cambridge: Cambridge University Press, 1999
10. Expert Group on Mental Health Policy. A Vision for Change: Report of the Expert Group on Mental Health Policy. Dublin: The Stationery Office, 2006