Epidemiology is defined as the study of the distribution and determinants of health-related stated or events in specific populations and the application of this study to control of health problems (Gordis 2003). Over the past year Cohort 7 has grown to appreciate the value of the epidemiology and the practical application of this knowledge. As current and future leaders in healthcare systems, it is important to not only to understand the concepts learnt in epidemiology, but to use these concepts in the drafting of policy, the designing of programs and in making contributions to national, regional and international healthcare systems. The three epidemiological concepts to be discussed are; estimating risk, study design and ethical & professional issues in epidemiology. The basics of each concept and its importance shall be outlined followed by a discussion of the perceived benefits to policy makers and populations at large and the application of each concept individually. For the purpose of this discourse, I have selected the chronic non-communicable disease, type 2 diabetes to illustrate the applications of the listed concepts through the eyes of a policy maker and programme designer. This paper shall be closed with a summary of the application of the concepts and a conclusion.
Concept I: Estimating Risk
Risk has been defined as the probability of an event occurring (BMJ). In our current course of study, epidemiology, risk is often used to express the likely-hood that a particular outcome will happen after a particular exposure. It is important to understand risk and exposure in the capacity of policy maker. Chronic-Non-Communicable-Disease (CNCDs) is a growing concern nationally, regionally and internationally. In Trinidad & Tobago the prevalence of diabetes is estimated to be as high as 1 in 5 of all adults (Ministry of Health 2010). Diabetes is the second leading cause of death and the leading cause of adult blindness in Trinidad & Tobago.
The measurements of risk are; absolute risk or incident rate, relative risk, attributable risk and odds ratio. According to Gordis 2003, absolute risk is the incidence of the disease in the population, i.e. the number of new cases of the disease in a specified population over a given time. The incidence of diabetes in Trinidad & Tobago has been estimated as 1,000 cases per year (John Hopkins 2012). This information about the absolute risk of diabetes has an important implication in public health policy formation. It tells the policy designer in the Ministry of Health that there would be an estimated 1,000 new cases of type 2 diabetes per year and so the current out-patient clinics for diabetics would need to be expanded.
With that number of new cases per year there will be a greater demand placed on the Ministry of Healths Chronic Disease Assistance Programme (CDAP) and more funding will have to be allocated to deal with diabetes. Since absolute risk gives no consideration to risk factors or exposure, it is necessary for the policy designers and planners to look at the other measurements of risk to formulate appropriate plans to reduce spending associated with the morbidity and mortality of this CNCD. This benefits the country as it improves the well-being of the human resource. Relative risk is defined as the probability of exposed persons developing disease compared to non-exposed persons developing disease (Gordis 2003) while attributable risk is the amount of a disease incidence that can be attributed to a given exposure. The odds ratio or relative odds can simply be defined as a measure of association between an exposure and an outcome.
It represents the odds that an outcome will occur given a particular exposure, compared to the odds of the outcome occurring in the absence of that exposure. Knowledge of the risk factors for type 2 diabetes is valuable in looking at the relative risk, attributable risk and relative odds of type 2 diabetes. A risk factor is a variable associated with an increased risk of disease (Burt 2001). The risk factors for type 2 diabetes are; family history of diabetes, increasing age, ethnic background, inactivity, metabolic syndrome, being overweight and history of gestational diabetes in women (Joseph 2010). In designing policies and programs to combat type 2 diabetes, there would be an attempt to target members of the population with these risk factors. It would be prudent to provide funding to institutions which are conducting studies to clarify relative risk, attributable risk and relative odds in diabetes as these studies would help in the understanding of the etiology of type 2 diabetes.
Concept II: Study Design
There are four basic study designs; cross-sectional studies, case-control studies, cohort studies and randomized clinical trials. As stated previously, it would be prudent to fund institutions conducting studies to clarify relative risk, attributable risk and relative odds in type 2 diabetes as such studies would aid in the understanding of the etiology of type 2 diabetes. In clarifying the etiology of type 2 diabetes in a given population better strategies for management and prevention of the diseases can be adopted. In the capacity of policy and programme designer, it is useful to have an understanding of study design so that the proposals for studies which can produce the greatest data on etiology in the shortest time-span can be selected for funding. In cross-sectional studies both the exposure and disease outcome are determined simultaneously for each subject (Gordis 2003). The prevalence of the disease can be determined with this type of study; hence the study can also be called a prevalence study. The prevalence of diabetes in Trinidad & Tobago is one in every five adults (Ministry of Health 2010).
Cross-sectional studies are useful to policy writers and programme designers as it provides a snap shot of how many individuals within the population have the disease. However the association with the risk factors does not prove temporal relationship. For the justification of policy and programmes, etiological relationships must be established. These etiological relationships can be justified through case-control and cohort studies. Case-control studies are useful in examining the possible relation of an exposure to a certain disease. At the beginning of the study individuals with the disease (cases) and individual without the disease (controls) are identified. The exposure of both of these groups is then compared. So in the case of type 2 diabetes, persons with type 2 diabetes can be identified (cases) then separated into two groups on the basis or exposure to a given risk factor. Persons without type 2 diabetes (controls) can also be identified than separated on the basis of exposure to the same risk factor. Then the two groups of exposed individuals can be compared. By identifying cases & controls and looking at exposure, the relative risk, attributable risk and odds ratio can be calculated.
Case-control studies are invaluable in finding the etiology of disease. In cohort studies the researchers select a group of individuals from a given population. These individuals are then categorized as either exposed or non-exposed. Cohort studies can either be prospective or retrospective. In prospective cohort studies the exposed and non-exposed individuals are followed forward in time and the development of disease is noted. In retrospective cohort studies the end result, i.e. disease or no disease is noted at the starting point. The researcher can then trace the individuals backwards through time to determine their exposure or non-exposure. Prospective cohort studies are expensive and time consuming as they may take many years to be completed. In the case of diabetes, it may take many years for exposure to lead to disease. Retrospective cohort studies may be better for proving causal relations in diabetes, but records may not be easily available.
The high prevalence of diabetes is a good justification for conducting a cohort study. Once again relative risk, attributable risk and odds ratio can be calculated. A randomized clinical trial is an experiment in which the effectiveness of a mode of treatment is evaluated. Cross-sectional, case-control and cohort studies are all observational studies. However, in randomized clinical trials, the effectiveness of treatment modalities are measured. Usually individuals for the study are assessed for eligibility before hand and subsequently randomly placed into one or an alternative treatment group. The merits of preventive strategies can best be illustrated by means of randomized clinical trial. Considerable work has been done in ascertaining the risk factors of type 2 diabetes. After review of the literature I have concluded that there is the need for more experimental studies for better management of type 2 diabetes. As a policy writer and programme designer it is critical to ensure that approvals are granted for ethically sound randomized clinical trials. It is important to note that a good knowledge of study design is essential to a policy makers/ programme designers. The type of study to approve for funding will undoubtedly be based on maximum benefit to the population, cost effectiveness and ethical considerations.
Concept III: Ethical & Professional Issues in Epidemiology
The ultimate objective of epidemiology, according to Gordis, is to improve human health. Ethical consideration must be high on the agenda in public health since epidemiological findings are socially relevant, often publically funded and the research is conducted on human subjects. As discussed previously, there are two broad types of studies in epidemiology; the observational studies which include the cross-sectional, case-control and cohort studies and the experimental study or randomized clinical trial. As a policy writer and programme designer, I am obligated to ensure that investigators and researchers obtain informed consent from their subjects, where possible, and that there is privacy and confidentiality. There is a need for research on type 2 diabetes to be conducted in Trinidad & Tobago and the wider region so that there is relevant and timely data for the implementation and improvement of policies for reducing the morbidity and mortality associated with type 2 diabetes.
There have been many studies which contribute to the body of knowledge compiled by the International Diabetes Federation. While there is merit in conducting observational studies, I believe that there must be more experimental studies aimed at improving the prevention and management of diabetes. In the design and execution of experimental studies, the rights of the individuals and the welfare of society must be balanced. Careful oversight of experimental research can protect individual confidentiality while ensuring that there is no conflict with the welfare of society. Even though there is the objective of improving human health, there is debate on how much of the findings should be made available to the subjects in both observational and experimental studies. While I believe that the findings of research should be held in the public domain, it is important not to create undue panic or hope of a miracle cure when publishing results.
Epidemiology is the study of the distribution and determinants of health-related stated or events in specific populations and the application of this study to control of health problems. Consequently the objective of epidemiology is to improve human health (Gordis 2003). The three epidemiological concepts discussed were, estimating risk, study design and ethical & professional issues in epidemiology using the disease type 2 diabetes for illustration. It is important for a policy writer/ programme designer to understand risk and the measurement of risk so that there are policies and programmes that benefit the greatest proportion of the population are designed and implemented in the reduction of the prevalence and incidence of type 2 diabetes and its associated morbidity and mortality.
Studies, both observational and experimental, should be encouraged but these studies must be conducted within the confines of ethics and professionalism. Ethics and professional are integral building blocks of study design since the findings are socially relevant, public funds are often used and the research is conducted in human subjects. There must also be publishing of the findings of these studies but researchers should neither create undue panic nor give false hope.
The three epidemiological concepts discussed for this paper were; estimating risk, study design and ethical & professional issues in epidemiology. These were discussed concepts through the eyes of a policy maker and programme designer using the disease type 2 diabetes for illustrations. Studying the distribution and determinants of health-related states is not simply a course that constitutes part of a masters degree that a student must pass or get over but rather a guiding principle to be incorporated into decision making, so that the application of this study can truly be used to control health problems. These health problems can range in simplicity from common childhood ailments to pandemics. Therefore participants in this course of study are expected to make sterling contributions to national, regional and international healthcare systems based on understand of concepts learned in epidemiology.
1. Burt BA. Definitions of Risk. Department of Epidemiology School of Public Health University of Michigan, 2001.
2. Center for Statistics in Medicine BMJ Statistics Notes. (Undated) Retrieved May 13, 2014. URL:http://www.csm-oxford.org.uk/index.aspx?0=1292
3. Gordis Leon. Epidemiology. 3rd edition. Philadelphia: Elsevier 2004.
4. Josepha Joseph, Johan Svartberg, Inger Nj¸lstad, Henrik Schirmer. Incidence of and risk factors for type 2 diabetes in a general population. The Troms¸ Study. Scand J of Public Health, 2010;38 (7):768-775. 5.
6. Last JM, ed. A dictionary of epidemiology. 4th edition. New York: Oxford University Press, 2001.