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In this chapter we describe in general terms what we mean by the equivalent terms multilevel analysis (MLA) or multilevel modelling. We place MLA in the context of public health and health services research. Most of our readers will be working in this field, and this book is specifically written for them. As public health and health services research is an applied research, it is strongly oriented towards solving practical problems in health, healthcare and health policy. Therefore we will also discuss the relationships between research on the one hand and policy and practice on the other. We end with some conclusions on the relevance of MLA for public health and health services research.
KeywordsMultilevel analysis Public health research Health services research Health policy Health system organisation Inequalities in health
The fact that we are willing to consider ‘Health in context’ means that people’s health depends on the context in which they live. This is a basic credo of social medicine and public health (Rosen 1993). Not only health and well-being but also health behaviour and healthcare utilisation depend partly on people’s personal resources and partly on shared resources and circumstances—in other words, their context. People’s personal resources can be their personal stock of health—their health capital in other words—as well as other more tangible resources. So if we talk about health, we are implicitly talking about two distinct levels: people and their context.
MLA makes it possible to handle this reality of health operating at different levels. Although MLA is a statistical method, it would be too narrow to restrict the teaching of multilevel modelling to statistical methods courses. Statistics is a tool to solve problems, so the methods should not be seen to be isolated from the problems themselves. In other words, if we want to understand MLA, we should also pay attention to the substantive fields of public health and health services research and to the origins of their research problems. Moreover, in sociology, a lot of attention has been paid to the relationships between different levels, from the micro level of individual people, via intermediate levels of families, schools and work organisations, to the macro social levels of cities or countries. Social science helps us to conceptualise these different levels and to decide which levels are relevant for certain research problems. Therefore, it is not only statistics that we will be dealing with in this book; theoretical considerations about levels and about human behaviour in context are equally important. We should add a third pillar to this book: study design and methodology. Between theory and statistics stand the study design and methodology—the way we design our research and collect data to test our theoretical ideas.
Importance of MLA for Research in Health and Care
MLA is important for research in the fields of public health and healthcare for two reasons. The first is substantive: many of the problems studied involve different levels or contexts. To analyse such problems with state-of-the-art methods, MLA is the most appropriate statistical tool. Secondly, research in the fields of public health and healthcare increasingly uses MLA. It is therefore important that even if you do not apply MLA yourself, you are able to understand research that uses MLA. Nowadays it is nearly impossible to understand, appreciate and critically appraise published articles in our field of research if you are not acquainted with MLA.
The pioneering development of MLA methodology has been in education where researchers have been interested in studies examining how pupil outcomes (such as examination scores) are related to both the characteristics of the pupils themselves and those of the schools (Aitken and Longford 1986; Snijders and Bosker 2012). The use of MLA has since been widespread in the overlapping fields of health services research, epidemiology and public health (Diez-Roux 2000; Leyland and Groenewegen 2003; Merlo et al. 2005a, b, c, 2006; Rice and Leyland 1996; Subramanian et al. 2003), assisted by the development of specialist multilevel software and the addition of multilevel capabilities to common statistical packages (de Leeuw and Kreft 2001). The educational example may be transferred to a public health context in several ways. For example, when studying outcomes in hospitalised patients, interest focuses on the roles played by both hospitals and patients. The individual and the workplace may both influence absence from work due to sickness. Regional differences in incidence of heart disease may reflect differences in the composition of populations and in the success of local health promotion programmes.
The Scope of Public Health and Health Services Research
Healthcare utilisation is traditionally the centre of attention in health services research. It is influenced by the demand for healthcare. The demand for healthcare is partly based on health—people with health problems tend to use health services—but not completely. There are also social and psychological influences on healthcare utilisation. People differ individually in the way they cope with ill health, and the threshold at which they will visit a healthcare professional also differs. There are also social influences, such as family or group norms as to when to invoke the help of others. The supply of healthcare also influences healthcare utilisation. The availability of hospital facilities, for example, influences their utilisation. And the organisation of healthcare facilities also affects utilisation; supply of and demand for healthcare exert their influence within an institutional context. This is the way in which the system is organised and funded. Whether or not general practitioners (GPs) have a gatekeeping role influences the utilisation, not only of the services that GPs provide but also of specialist services. Financial accessibility, in terms of organisation in systems of insurance or other funding of healthcare, also influences utilisation. Again we can say that these influences can be individual characteristics but often they are group- or population-level characteristics. Countries differ regarding the structure of their healthcare system, regions differ in the supply and mix of services, and social groups differ in how quickly they invoke healthcare.
Figures 1.1 and 1.2 also show the relationship between public health research and health services research. In public health research, the utilisation of health services is one of the determinants of health whilst in health services research one of the influences on healthcare utilisation is ill-health, and one of the outcomes of health service utilisation is the creation of health. Both public health research that does not take healthcare into account as an input and health services research that does not take health into account as an outcome can exist.
This brief discussion of the scope of public health and health services research has drawn our attention to different influences. Researchers with different educational backgrounds can study each of these influences on their own. Public health and health services research is populated by researchers who studied medicine, health sciences, epidemiology, psychology, sociology, statistics, human geography, economics, political science, etc. (and we must still have forgotten some). This diversity is the reason why we discuss rather broad substantive and theoretical issues in the first two chapters of this book. This ensures that we have a common understanding of the kind of research we are doing before proceeding to the statistical approach.
Research and Policy
To get a better feeling for this extended policy and research cycle and to illustrate the importance of different levels in studying problems in policy and practice of healthcare, we will spend some time on a very broad grouping of policy problems.
Governments have a responsibility for the health of their subjects. In the Netherlands, for example this responsibility for protecting and improving population health is part of the Constitution. Governments take this responsibility by designing and implementing policies. Some of these policies are directly related to health, whereas others are intended to improve healthcare. As the history of public health shows, policies directed towards standards for housing quality and public services in areas such as waste disposal and clean water supply have been very important. Often these are policies that originate outside the direct jurisdiction of ministries of health. They require crosscutting policies and analysis of the health impacts of sector-specific policies (Puska 2007).
Increasing the coherence and responsiveness of the system
Diminishing inequalities in health and in access to healthcare
Increasing the efficiency of the system (stewardship)
We use these three aims because, basically, most social systems are concerned with problems of coherence and responsiveness, inequalities and efficiency in one way or another, and healthcare is no exception. For example, a country’s educational system can be seen as trying to cope with these three basic problems: the way different types of school are tuned in to different educational needs, geographical and social inequalities in access to schooling and the efficiency of teachers and educational programmes. Therefore, we might get our inspiration to develop research in the healthcare field by looking at experiences in other sectors of society. We might also look at more general theories of how societal systems are organised or about the causes of inequalities. So we might use this insight in a horizontal way—looking at other sectors—or in a vertical way—looking at more general theories. An example of a book that does both is ‘The spirit level: why more equal societies almost always do better’ (Wilkinson and Pickett 2009).
Going back to healthcare, the emphasis that is placed on each of these three instrumental aims may vary over time or differ between countries (Tenbensel et al. 2012). If we look at the past few decades, we could say that in the 1970s the emphasis was on structuring the healthcare system, by strengthening primary care and by using planning as an instrument (Saltman and Von Otter 1992). In contrast, efficiency and stimulation of evidence-based healthcare were much more at the centre of policy attention during the 1990s (Sackett et al. 1996). The performance movement in healthcare is also intended to increase the efficiency of the system but performance indicators of healthcare in themselves, such as those developed by the World Health Organization (WHO) for the World Health Report 2000 (WHO 2000), try to incorporate indicators of inequality and responsiveness. Inequalities in access to healthcare are central to a model, developed in the early 1970s in the USA, called the Andersen–Newman model (Aday and Andersen 1974). This model looks at and subsequently analyses the influence of the need for healthcare; predisposing variables, such as attitudes about health and healthcare; and enabling variables, such as income or insurance status, and is still often used. Inequalities in health have featured prominently on the political agenda over the past decades from the Black report (Department of Health and Social Security 1980) to more recent reviews of the state and extent of inequalities (Commission on Social Determinants of Health 2008; Marmot Review 2010).
These aims of health policy give us a basic classification to enable us to position our own research problems. We can think of examples of a research problem addressing one of these central aims of health policy. In doing so, we will see that again different levels are involved. The central aims can be used to introduce the relationships between macro, intermediate and micro levels, and the idea is that more than one level is usually involved when you analyse a problem. We will briefly go through each of the three instrumental aims.
In these examples, we have used three different levels and named the higher two intermediate and macro. It is important to realise that there is no ‘law of three levels’. The number of levels in any study depends on a combination of theoretical analysis and practical considerations of data collection or availability. What is micro or macro depends on your point of view. Although the micro level is often the level of individuals, we will see in Chap. 4 that the micro level or lowest level in a multilevel analysis can also be a number of repeated observations on the same person. The lowest level can also be a small area, for example when we do not have access to individual health data for reasons of data confidentiality. In such a case we might obtain small area data and analyse them within a higher level of regions or countries. The macro level is also relative. In some research problems, this level might be formed by countries, but in others by GP practices.
The issues we have raised in this introductory chapter relate directly to the philosophy behind the book. Firstly, we feel that it is important to try to integrate substantive issues, methodology and statistics. Secondly, these substantive issues relate to the field in which we are working and our approach: application, policy and practice oriented. Thirdly, MLA has a close correspondence with the substantive issues; health and healthcare are context dependent. And, finally, we have to learn to think in multilevel concepts: to develop hypotheses, conceptualise contexts and define levels.
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