Epidemiology is the science that studies characteristics and causes of the spread of diseases in the community in order to apply the acquired knowledge to solve problems in health care. Epidemiological methods are investigation methods for morbidity, illness, and disability evaluation according to the sample surveys of the individual groups and populations.
Therefore, deep understanding of the principal features of basic epidemiological study designs is an observable value during adequate implementation of them in the study with concrete purpose and objective. The present research consists of introduction data about the purpose of some epidemiological study designs, general view on the most common and popular structure of implemented studies, identification and critical view on benefits and shortcomings of each of them, and relevant conclusion. Critically observation as a purpose of this paper will help evaluate epidemiological study designs with specific reference to their strengths, weaknesses, and circumstances under which certain designs are the preferred option.
Epidemiological Study Designs
Epidemiological methods include both unique research methods and implemented methodological techniques (entomological, historical, geographical, statistical, and others), according to epidemiological purposes, specific orientation, and principal design of the study. Different epidemiological study designs solve oriented questions. Some design resolves the definite access to the survey of ailments with the use of verisimilitude hypothesis, statistics, and specific methods for scientific experiments. Another design of the study was created to mount a cause-effect connection by testing assumptions about the occasions of sickness and its prevention. Other designs are tools for management of decision-making in public health based on scientific data. Also, peculiar features of epidemiological designs work on the evaluation of etiological hypotheses of the development of certain diseases (search pathogens or risk factors). Some of them work on the analysis of the effectiveness of interventions (diagnostic tests, medical technology, health interventions, etc.). However, each epidemiological study design has its purpose, as well as its strengths, weaknesses, and circumstances under which certain design is the preferred one.
The main designs of epidemiological studies are observational study, descriptive study, analytical (cross-sectional, cohort, and study of "case-control") study, hospital control design, communal (public) study, and experimental research. Different epidemiological designs are based on the identification of distinction in the vitality state of personalities and population in situations of exposure to different compounds in comparison with the control groups. Such studies are based on observations of the natural folding events. Therefore, the main difference between the experimental and epidemiological analysis is how the base is formed by the data being analyzed. In the pilot study, the experimenter actively creates a group of objects for future analysis, acting on the body estimated factor in the required conditions. In epidemiological studies, the investigated impact factor is not regulated by the researcher. Investigator controls only the steps of selecting representative groups of subjects from the population and selection of adequate methods for the information analysis. Nevertheless, each group of epidemiological study designs has its advantages and disadvantages.
Benefits and Shortcomings of Different Epidemiological Study Designs
Environmental studies are based on analysis of the current health statistics for the subsequent determination of the relationship between exposure to factors operating systems and public health. A simple description of the health status on the basis of medical and demographic statistics is the first stage of the epidemiological study. This is so-called descriptive epidemiology. The statistical analysis reveals the areas of research, identifies the populations exposed to various risk factors, as well as proposes a hypothesis about the possible cause-effect relationships to further test it in analytical epidemiological studies. Benefits of environmental epidemiological studies are determined by the possibility of using existing data. Therefore, such opportunity can substantially diminish time and outlay of the research to examine the multifold population. It makes possible identification of a moderate or even a small but statistically significant increase in risk. The hindrance of this variety of investigation is that the connection is sited at the population level, not necessarily at the individual level.
Transverse (cross-sectional) study is performed to measure the health of the population due to different adverse influences. This method of research is not applicable to the study of rare diseases, including cancer, because it is impossible to generate the necessary largest group of persons exposed and unexposed to carcinogens to identify any significant difference.
Case-control study includes the group with the disease and the control group (reference group) without the ailment. These studies compare the two groups regarding the possible causes of the indisposition and exposure to a harmful factor. Detection of greater proportion of persons exposed to the studied factor than in the control group indicates that there is some connection between the development of the disease and the influence of this factor. Studies of case-control are relatively ordinary in execution, economical, and widely used for the analysis of causes of diseases, especially rare, such as separate localization of malignant tumors. Case-control study takes into account the maximum effect and other factors affecting the result to avoid “confusing” factors. The study is usually retrospective, and the group surveyed only or those who are at the beginning of the study had already developed the diagnosed form of the pathology. In this regard, the method cannot be applied to assess the impact of real-time environmental factors on health. Vulnerable point of the study is a collection of information about the nature of the impact factor being studied. Sources of such information are not always entirely reliable (professional card, sick list, and other similar documents). Another drawback of the method is a high probability of underreporting of additional factors considerable for the formation of the estimated pathology.
Cohort studies provide complete information about the etiology of diseases and allow quantifying the risk of their development. Cohort (group) is formed from healthy individuals exposed to any influence, which is then observed for a definite time in order to identify it in cases. This study needs the greatest amount of time and money for its adequate implementation. The advantages of the cohort study lie in the fact that its result allows objective view on the real effects of the determined risk factor in the investigation group. Cohort studies are used for observation of the relatively rare exhibits of the careful selection of individual groups based on the nature of exposure. A wide range of pathologies associated with exposure study can be researched. During the cohort studies, detailed information is obtained on confounding factors that allow controlling either at the planning stage or in the analysis of data. However, this method of research has its shortcomings. It requires considerable coverage of the large contingent of people and is less common than the study under a small group. The study takes place over a long time (years), and the results are not known for a long time (until the end of follow-up). People included in the cohort usually are not under daily observation, so for permanent control over them required. Cohort studies have a high cost of research, which depends on the type of cohort (historical or current cohort). The duration of the cohort studies is greater than for all other types of studies. Especially, the long period is required during a prospective cohort tracking.
Experimental studies are used to examine the differences in the predominance of infirmities before and after the exposure conditions. Such studies can actively influence the conditions of their conduct. The data is usually achieved by studying the state of working before and after the implementation of preventive measures. The significance of experimental epidemiological studies is particularly high in confirming the causal nature of the relationship, the impact of the disease, and in assessing the prevention programs. Validity identified in epidemiological studies of causality depends on the type of research and increases in the order in which they appear.
Communal public epidemiological studies arrange for studying diseases initiated by social conditions. These diseases are tuberculosis, sexually transmitted diseases, and heart pathologies, the development of which is determinated by social factors. The disadvantages of this type of epidemiological studies should include impossibility of randomization and the need to assess the effect of specific methods derived from some intervention.
Hospital control designs provide study of the control groups that are assuredly accessible to the survey. Finding the control subjects in one place reduces transportation time and costs, facilitating the survey. Disadvantages of hospital controls include a higher probability of using medicines that affect health. These designs cannot trace the impact of such probabilities. It is known that during hospital controls study, the control may be confused due to a multifold number of systematic errors (selection of patients to the hospital according to nosology, disease severity, social status, etc.).
Quality of epidemiological information is determined by the accuracy and completeness due to the peculiar form of design. Reliable information is the data as closely as possible to the studied phenomenon. The notion of completeness of the information includes its volume and nature (diversity, versatility) necessary to conduct the study. The perfect fulfillment of these requirements, in most cases, is unattainable. However, in each circumstance, the researchers should collect the most complete and accurate information, comprehensibly realizing that neither sophisticated statistical methods nor logical construction cannot correct errors in data collection. Often, in the works based on complex medical and hygiene surveys, significant errors in planning studies, improper use of epidemiological methods, the shortcomings of statistical data processing and / or submission to print are found. Therefore, only adequate choice of epidemiological study design provides assessing of the prevalence and intensity of major dental diseases, identification of the need for their prevention and treatment, and the set of quantitative and qualitative objectives for healthcare and for the industry that produces equipment, materials, and medicines.