Original article
Use of a cross-sectional survey to estimate outcome of health care: The example of anxiety and depression

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Abstract

Our study proposes that a population-based cross-sectional survey can be used to estimate the outcome of health care by linking general practice morbidity records to the survey. Using the example of anxiety and depression to test this idea, we conducted a survey of an adult population registered with one general practice in the UK. The Hospital Anxiety and Depression (HAD) questionnaire was used to identify cases and controls. After mailing to a randomly selected adult population of 4002, there was an adjusted response rate of 66% (n = 2,606), with 416 (16%) high-score cases, 506 (19%) medium-score cases, and 1684 (65%) low-score controls. All cases were compared with a sample of controls (n = 450). In the 12 months before the survey, the high-score case group had experienced significantly higher GP contacts (n = 377 [91%] versus 354 [79%]), diagnoses for anxiety or depression (119 [29%] versus 21 [5%]), and related drug treatments (111 [27%] versus 22 [5%]) compared with the control sample. Most of the diagnoses and drug treatments had been initiated at least 9 months before the survey. The linkage between the survey and the clinical records suggested that the health outcome of previously identified anxious and depressed patients was poor, with an estimated two-thirds who will not have fully recovered within an average of 9 months. This study demonstrates the potential for using cross-sectional population surveys to estimate not only the need for health care but also the outcome of health care.

Introduction

Population surveys are an important epidemiological tool because they are based on the principle that the sample of the target population surveyed is unselected by health care setting or membership of particular groups. Such survey methods are used to estimate the health care needs for a given problem in a population. In the particular example of neurotic disorders, the Epidemiological Catchment Area study [1] and the UK OPCS survey [2] have estimated the prevalence in the population for these conditions at approximately 15% and this figure would represent the overall likely need for health care.

Outcome of health care, in contrast, has been traditionally estimated by prospective studies, in particular randomized controlled trials. The generalizability of the results of trials is often limited by the selectivity of their participating populations, and a complementary method is to perform observational follow-up studies to determine what happens to a broad group of patients who receive the treatment or intervention in actual practice. Examples of such approaches in the field of neurotic disorders include the World Health Organization (WHO) international study on depression outcome [3] and the study of the influence of adherence to antidepressant treatment guidelines on subsequent relapse and recurrence of depressive illness [4].

So traditionally, distinct and different approaches have been used to determine need and outcome. Assessing both are key objectives in delivering effective health care. Local health care systems have adopted the survey as one approach to measuring need, but methods to assess outcome of care are less easily translated from research to a health service environment. It is curious that epidemiological surveys are assumed to identify need for health care, but will actually include groups of people who have already received health care, and who at time of the survey have either recovered or not recovered, as well as people who have symptoms but have not received care. All of this means that the traditional survey of need is also presenting the observer with a picture of the outcome of health care already received in that population.

To use a survey both as a measure of outcome of health care as well as health need, we have to know the prior health care provided for the condition. In the UK, the clinical general practice records of the population are continuous, irrespective of whether the patients move practice, and are life-long. More than 95% of the UK population are registered with general practitioners who provide access to most health care services within the National Health Service. Hence, these records can provide data on all clinical diagnoses and treatments in the registered population. By relating the previous health records of individuals to a cross-sectional survey, the survey results will represent an estimate of the outcome of earlier diagnoses and health care. Few studies have attempted to use retrospective case-control methods to assess outcome of health care, except in the field of screening [5] and isolated investigations of other topics [6].

Our study used a postal survey to assess the prevalence of health care needs for anxiety and depression in a population registered with a general practice in the UK, and we hypothesized that such a survey could also be used to estimate the outcome of health care. We used general practice data as the source of historical information about health care, and applied it to the health status determined by the population survey, to estimate the current outcome of primary health care for anxiety and depression in this population.

Section snippets

Design

The study was a population-based case-control study. There were two phases: phase 1 was a postal survey of the registered practice population and phase 2 a retrospective 12-month review of practice-held records of a sample of the surveyed population. Survey subjects who had current high or medium scores on a scale of anxiety or depression symptoms were compared with a control group of subjects with low scores.

Study population

As more than 95% of the British population are registered with a general practitioner,

Phase 1: Population survey

In the total survey sample of 4002, there were 34 patients who were temporarily registered patients, i.e., less than 3 months with the practice, so the adjusted survey response rate after the exclusion of this group was 66% (n = 2606). The number of patients with a high HAD score in the survey responders for anxiety or depression was 416 (16%); 506 (19%) patients had a medium score; and there were 1684 (65%) controls. The prevalence of probable anxiety and depression as shown by the high score

Study findings: population survey as an estimate of health care need

The questionnaire survey confirmed the high prevalence of anxiety and depression symptoms in the adult UK population. Figures for the high score group were comparable to those of other studies 1, 2, which have estimated the prevalence of neurotic disorders such as anxiety and depression at approximately 15% in the population. The associated demographic characteristics also confirm results from other studies 1, 2.

Study findings: population survey as an estimate of health care outcome

Patients with a high HAD score were more likely to have contacted the GP for any

Acknowledgements

North Staffordshire Health Authority supported UTK in a Public Health post during the project year and the Royal College of General Practitioners Scientific Foundation Board Grant funded part of the project. We are very grateful to all the patients and staff of the study practice. We would also like to thank Rob McCarney for his help in the survey data collection, Rhian Hughes for assistance in record data collection, and Paul Trinder for his comments on the earlier drafts of the paper.

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