Comparison of prevalence of schizophrenia among residents of hostels for homeless people in 1966 and 1992

Subjects and methods

The residents of hostels or common lodging houses form only one subgroup of the total homeless population, which also includes the “roofless” and residents of bed and breakfast accommodation. No attempt was made to include these other groups in this study.

1966 Survey*Rf 4*

Sample--Priest randomly sampled 98 subjects from the residents of three common lodging houses in the Old Town of Edinburgh (Salvation Army, Grassmarket Hostel, and Greyfriars Hotel).

Assessments--All interviews were performed by Priest. The relevant parts of the interview for the present study consisted of a semistructured interview, including questions on demographic and social data, history of employment, contact with the law, contact with welfare agencies, and psychiatric history; clinical interview; and the symptom sign inventory,6 an early example of a standardised psychiatric interview consisting of a battery of 80 questions to produce a psychiatric diagnosis. Subjects received a packet of cigarettes on completing the interview. Clinical diagnoses of schizophrenia were made on the basis of all information available and classified as probable and definite. Most subjects diagnosed as suffering from schizophrenia experienced hallucinations, paranoid delusions, and replied affirmatively to the question designed to elicit primary delusions. Cases classified as probable schizophrenia were not counted as schizophrenic for the purposes of the present study.

1992 Survey

Preparation--Careful preparation and field work is necessary in surveys of homeless people.7 8 Before the survey all the hostels for the homeless were visited by the team to gain the cooperation of the staff. The study was described to the Southside and Old Town com- munity care forum, a body representing all agencies concerned with providing services for homeless people in the area. JG and RN were already familiar with the hostels through running a psychiatric clinic for homeless people, and GY had previously worked in the Cowgate day centre, a facility for the homeless population of Edinburgh.

Sample--The aim of sampling was to achieve a representative sample of the homeless people resident in hostels in Edinburgh Old Town and Leith. We expected that there would be an increase in the prevalence of schizophrenia in the 1992 sample. The power of the investigation to detect an increase in the prevalence of schizophrenia from 25% to 50% at P< 0.05 by using samples of equal size (the response rate in 1966 limited this to 79 observations in each sample) was calculated to be about 90%.9. We therefore decided to aim for a sample size of at least 150 to allow for a potential 50% non-response rate, which was considered possible in this population. The sampling frame comprised all subjects resident in nine hostels in Edinburgh on 25 May 1992. The hostels included in the sample were Jericho House, Leith Lodging House, the People's Palace, Cranston Street, Salvation Army, Greyfriars Hotel, Stopover, Cyrenians, and Bowfoot. A 50% random sample was taken from the listing for each hostel. A sample of 198 was produced.

Assessments were conducted by two trained interviewers (SB and GY). Each assessment typically lasted one to three hours and consisted of the administration of two instruments. Firstly, we used a semistructured interview designed specifically for the study covering demography, use of services, and forensic history. Questions from Priest's study in 1966 were included in the sociodemographic schedule to allow direct comparison between the two samples. Secondly, we used the present state examination,10 a widely used semi-structured interview for the rating of psychiatric symptoms which has been shown to be reliable in community screening when used by non-medical interviewers.^{11 12} Because we expected a high prevalence of schizophrenia and because the reliability of the examination in such subjects when used by nonmedical interviewers has not been shown,11 all interviews were audiotaped and all subjects with any positive symptom ratings and a random sample of those with none were rerated by a psychiatrist (JG and RN). Schizophrenia was diagnosed according to the Diagnostic and Statistical Manual of Mental Disorders, third edition, revised (DSM-III-R)13 on the basis of all relevant information--that is, the present state examination, history, and case notes when available. Both interviewers had substantial previous experience of subjects with psychotic illnesses (one had worked as a support worker for people with long term mental health problems and the other had worked in a day centre for the homeless) and also received further training. The interviewers and psychiatrists had formal training in administering the present state examination before the study, which ensured high agreement between assessors.

Response rate--Previous studies have found a high rate of non-response in similar populations. To assess the bias introduced by non-response as much information as possible was obtained on non-responders. This usually included age and sex. Information from the Lothian psychiatric case register was obtained for the whole sample to provide validation of the self reports of the subjects and also to provide an estimate of the psychiatric morbidity among the non-respondents. The register is a computerised case register which has recorded contacts with inpatients within Edinburgh since 1970 and all contacts with the psychiatric services within Edinburgh and part of Lothian since 1978. All subjects were paid £5 on completion of the interview, and the interviews were performed between 25 May and mid-September 1992. The study protocol was passed by the ethics of medical research (psychiatry and clinical psychology) subcommittee of Lothian Health Board.

Variables examined

Table I shows the variables we could examine on the basis of comparable information. These included several which probably altered between 1966 and 1988--in particular, the age distribution, unemployment rates, and the prevalence of schizophrenia. During the period between the two studies there were changes in the hostels themselves. Several of the hostels from which the 1966 sample was drawn had closed and new hostels had opened. Hostels catering for particular groups--for example, Stopover, for young homeless people--opened in response to changing needs. Although the 1992 sample was representative of the population resident in hostels at that time, some of the observed differences between the two samples are possibly because of sampling bias. A further dichotomous variable was therefore introduced to discriminate between the subjects who lived in the hostels open in 1992 that most closely resembled those from which the 1966 sample was drawn and the subjects residing in more recently opened hostels, which often catered for particular subgroups. This restricted the 1992 sample to subjects resident in the Greyfriars Hotel (run by the district council), the Salvation Army Hostel for men, the Peoples' Palace (Church of Scotland), Jericho House (Benedictine Order), and Cranston Street hostel for women. All these hostels are in Edinburgh Old Town and have admission policies and facilities broadly comparable with the hostels sampled in 1966.

A second diagnostic variable was constructed to allow comparison of non-respondents from the 1992 survey to give a measure of response bias. This used diagnoses on non-respondents estimated from infor- mation from the psychiatric case register and hospital case notes when available.

Statistical analysis

The hypothesis that there was no difference between the prevalence of schizophrenia in 1966 and 1992 was tested by using univariate logistic regression, which was performed with the EGRET computer program.14 The dichotomous dependent variable was the presence or absence of schizophrenia. The characteristics of the subjects may have changed in several other ways apart from any possible change in the prevalence of schizophrenia. Homeless people today are often younger than those in the past.^{15 16} Timms and Fry found a higher incidence of schizophrenia among the longer stay residents in a Salvation Army hostel in London.17 Changes in the profile of homeless people in variables such as these could potentially explain any change in prevalence found in the present study.

The findings in table I show several possible changes between the two samples. In particular, in the 1992 sample a higher proportion of the subjects seemed to be aged under 40 years, more subjects gave psychiatric illness and alcohol or drug abuse as the reason they were homeless, and more gave a history of admission to psychiatric hospital. In 1992 fewer subjects were resident in the hostels selected as being strictly comparable with those in existence in 1966. Age, duration of homelessness, duration of residence in the current hostel, current hostel and prison history were selected as potential confounders. For the purposes of the analysis we had to reduce the data into dichotomous variables. Age was dichotomised into <40 years v. >/40 years; duration of homelessness, duration of residence in current hostel, and duration of unemployment were each dichotomised into < 1 year v >/ 1 year.

To model the effect of these other changes on the crude odds ratio for the period the univariate logistic regression model was extended by fitting, one at a time, terms representing the dichotomised variables selected as potential confounders. At each extension, the effect of adding the term on the odds ratio for period was assessed. Terms which substantially (defined as a change of at least 10%) altered the estimate of the odds ratio for period were retained in the model. Only observations with complete data were used for fitting this model. Finally, by using the variable constructed with the data from the register to estimate diagnoses in the 1992 cases with missing diagnostic data, we calculated a univariate odds ratio to estimate the bias introduced by the non-respondents. This was then adjusted, when possible, for the effects of those variables which were included in the main analysis.