Research
Prospective validation of a predictive model that identifies homeless people at risk of re-presentation to the emergency department

https://doi.org/10.1016/j.aenj.2011.12.004Get rights and content

Summary

Objective

To prospectively evaluate the accuracy of a predictive model to identify homeless people at risk of representation to an emergency department.

Methods

A prospective cohort analysis utilised one month of data from a Principal Referral Hospital in Melbourne, Australia. All visits involving people classified as homeless were included, excluding those who died. Homelessness was defined as living on the streets, in crisis accommodation, in boarding houses or residing in unstable housing. Rates of re-presentation, defined as the total number of visits to the same emergency department within 28 days of discharge from hospital, were measured. Performance of the risk screening tool was assessed by calculating sensitivity, specificity, positive and negative predictive values and likelihood ratios.

Results

Over the study period (April 1, 2009 to April 30, 2009), 3298 presentations from 2888 individuals were recorded. The homeless population accounted for 10% (n = 327) of all visits and 7% (n = 211) of all patients. A total of 90 (43%) homeless people re-presented to the emergency department. The predictive model included nine variables and achieved 98% (CI, 0.92–0.99) sensitivity and 66% (CI, 0.57–0.74) specificity. The positive predictive value was 68% and the negative predictive value was 98%. The positive likelihood ratio 2.9 (CI, 2.2–3.7) and the negative likelihood ratio was 0.03 (CI, 0.01–0.13).

Conclusion

The high emergency department re-presentation rate for people who were homeless identifies unresolved psychosocial health needs. The emergency department remains a vital access point for homeless people, particularly after hours. The risk screening tool is key to identify medical and social aspects of a homeless patient's presentation to assist early identification and referral.

Introduction

The experiences of homelessness and poverty are inextricably linked as complex co-morbidities, financial hardship and barriers to health care, creating a cycle into homelessness that is difficult to interrupt.1 The homeless population is difficult to identify and engage. People who are homeless often have multiple health issues including drug misuse, mental illness and chronic disease.2, 3, 4 Lack of appropriate housing and social support means that many are frequent users of emergency departments (EDs).5

The ED is a 24-hour service, which primarily treats people with acute illnesses and injuries. Homeless people continue to account for a significant proportion of frequent ED users despite the development of outreach and case management programs for people with complex care needs.6, 7 Frequent ED users utilise a disproportionate amount of resources,8, 9, 10, 11, 12, 13 placing added pressure on acute care services, exacerbating prolonged waiting times in EDs and hampering access to inpatient beds.14, 15 Frequent ED users are vulnerable,16, 17, 18, 19 have complex health care needs,9, 16, 20, 21, 22, 23, 24, 25, 26 and suffer higher levels of mental illness,27 injury,28 morbidity, mortality,21, 27 social disadvantage16, 18, 21, 22, 24 and homelessness4, 25 than infrequent ED users. A study conducted in an Australian ED noted the total ED presentation over two years was 64,177 with a re-presentation rate of 17.3% (n = 11,128) of visits and 14.0% (n = 5718) of all patients.29 The odds of re-presentation increased three-fold for people who were homeless compared to those living in stable accommodation (adjusted OR 3.12; 95% CI 2.86–3.40).29

Research is needed to develop a way of identifying those people who are at risk of re-presentation to the ED to assist in early identification of health problems and referral. McCusker et al.30 tested a screening tool in the ED specifically developed for the elderly (ISAR) and found that it could be used to identify elderly patients who subsequently experience high acute care hospital utilisation as well as adverse health outcomes after presentation to the ED. This study aims to broaden the scope beyond the elderly and evaluate a predictive model that had been developed31 to identify key characteristics associated with ED re-presentation to facilitate early identification and referral.

Using a large hospital administrative dataset, we previously identified key patient characteristics associated with ED re-presentation in a homeless population and subsequently developed a risk screening tool to predict the likelihood of re-presentation to the ED within 28 days of discharge from hospital (Fig. 1).32 The aim of the present study was to examine the ability of the risk screening tool to predict risk of re-presentation to the ED using a prospective sample and to compare the ED characteristics of the prospective sample with a previous retrospective sample of homeless people.

Section snippets

Theoretical model

The risk screening tool was underpinned by the Behavioural Model for Vulnerable Populations (BMVP) which provided understanding about the complex range of factors associated with a person's utilisation of health care services specifically for social disadvantaged populations.33 The nine variables within the tool covered all four domains of the Behavioural Model. First, age, known next of kin and pensioner status are part of the environmental influences. Second, the number of medications and

Results

The level of risk score ranged from six to twenty-nine with the mean 18.19 (CI, 14–22). Three separate calculations of sensitivity and specificity were calculated using cut-off scores for high risk of re- presentation as ≥14, ≥17 and ≥19 (Fig. 3). A cut-off of ≥17 yielded the best balance between sensitivity 98% (95% CI, 0.92–0.99) and specificity 66% (95% CI, 0.57–0.74) and resulted in an area under the ROC curve of 0.79 (95% CI, 0.74–0.86), a PLR 2.9 (95% CI, 2.2–3.7) and a NLR of 0.03 (95%

Discussion

The predictive model was able to accurately identify the risk of re-presentation for those people who were homeless who presented to the ED during the study period. Risk screening tools are utilised in health care settings for many clinical applications. The assumption that risk screening tools are better than clinical judgement and that they will be well utilised in the clinical setting are two main concepts that apply to all tools. The application and usability of the tool in the clinical

Strengths and limitations

The study involved analysis of clinical audit data for presentations to the targeted hospital and it was not possible to identify those people who may have presented to other hospitals after attending the study hospital. This study was based in a single hospital site, which is located in a large Australian city with a population of 3.9 million people. While the study was conducted at a single inner-city ED in Australia, this work has the potential to be replicated in other Australian EDs. The

Conclusion

A defined understanding of re-presentation and homeless status underpinned by a risk screening tool has clinical relevance to assist in early recognition of risk factors and targeting specific resources. This risk screening tool has the capacity to clearly identify key factors that highlight risk of re-presentation within 28 days. The utilisation of administrative data in conjunction with clinical data is an effective method to identify the risk of re-presentation in the homeless population. It

Provenance and conflicts of interest

Marie Gerdtz is a Deputy Editor of the Australasian Emergency Nursing Journal but had no role to play in the peer-review or editorial decision-making associated with this manuscript whatsoever. All other authors reported no conflicts of interest. This paper was not commissioned.

Funding statement

Financial support was provided through the Australian Research Council Linkage Project Scheme, project number: LP0453587. Financial support was also provided by Research Endowment Fund, St. Vincent's Health.

Research ethics statement

This paper reports the findings of a research study that adhered to the National Statement on the Conduct of Human Research by the Australian National Health and Medical Research Council and has been approved by the institutional review board of the participating hospital, the participating community based organisation that deals with the needs of homeless people, and the university.

Authorship

GM, EM, MG, MK, TW conceived and designed the study. GM, EM, MG and TW obtained research funding. TW and MK supervised the conduct of the trial and data collection. GM undertook recruitment of patients and managed the data and analysis, including quality control. GH and DD provided statistical advice on study design and reviewed analysis. GM drafted the manuscript, and all authors contributed substantially to its revision. GM takes responsibility for the paper as a whole.

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