Lecture 5 Typology 1 Types of Epidemiological Studies PDF

Made with Xodo PDF Reader and Editor Types of Epidemiologic Studies (Typology) Community Medicine & Epidemiology Dr. Sanabel Barakat Year 3 – semester 1 BDs., MSc., PhD., JDC. Week 5...

Made with Xodo PDF Reader and Editor Types of Epidemiologic Studies (Typology) Community Medicine & Epidemiology Dr. Sanabel Barakat Year 3 – semester 1 BDs., MSc., PhD., JDC. Week 5  Made with Xodo PDF Reader and Editor Learning Objectives 1.Classify epidemiological studies 2.Define observational studies 3.Identify different types of observational studies 2  Made with Xodo PDF Reader and Editor Outline Classification of epidemiological studies Discuss Observational Descriptive studies case report/series cross-sectional (survey) Ecological studies Time series studies 3  Made with Xodo PDF Reader and Editor The key elements and determinants of outcomes of war are fixed even before it is fought Designing a research study is not a simple task. Success of an epidemiological study is determined at its initial planning stages 4  Made with Xodo PDF Reader and Editor Introduction In epidemiological studies it is essential to have a clear definition of: The case of the disease/condition being investigated, (symptoms, signs or other characteristics indicating that a person has the disease/condition). An exposed person, (the characteristics that identify a person as being exposed to the factor under study, (exposure, risk factor or suspected causal). In the absence of clear definitions of disease/condition and exposure, great difficulties are likely to be experienced in interpreting the data from an epidemiological study. 5  Made with Xodo PDF Reader and Editor Classification of Epidemiological studies Epidemiological studies can be classified according to different perspectives, and it is not always possible to establish consensus on the forms of classification. 6  Made with Xodo PDF Reader and Editor Classification of Epidemiological studies Descriptive (case report/series, cross-sectional According to (survey), ecological, time series studies) objective : Analytical (case-control & cohort studies, trials) Observational (case report/series, cross- According to sectional (survey), ecological, time series studies, case-control & cohort studies) methodology: Experimental (RCTs, Field trial, community trial) 7  Made with Xodo PDF Reader and Editor Classification of Epidemiological studies First Classification of epidemiological studies is based on the scope of the study objectives to descriptive or analytical studies. The precise definition of the objectives is a fundamental condition for the planning of the study. The type of study is a consequence of the research objectives. 8  Made with Xodo PDF Reader and Editor Classification of Epidemiological studies The study is DESCRIPTIVE when the researcher solely intends to describe the pattern of the occurrence of diseases with variables related to the person, time, and place. The study is ANALYTICAL when specific hypotheses of causal association between variables are tested 9  Made with Xodo PDF Reader and Editor Classification of Epidemiological studies Second: Classification of epidemiological studies according to their methodological aspects, with particular reference to the mechanisms used for data collection and the form of their organisation in time. In this respect, studies are classified into experimental (or intervention) studies, and observational studies. 10  Made with Xodo PDF Reader and Editor Classification of Epidemiological studies Observational studies: Are those in which the researcher does not intervene, that is, does not artificially introduce an exposure factor and only reports the data that could be gauged through observation Experimental studies differ from observational studies because the researcher is intervening in the studied population, controlling some exposure effect. 11  Made with Xodo PDF Reader and Editor Classification of Epidemiological studies Epidemiological studies classification According to objective : Descriptive (case report/series, cross-sectional (survey), ecological, time series studies) Analytical (case-control & cohort studies,) According to methodology: Observational Descriptive (case report/series, cross-sectional (survey), ecological, time series studies) Analytical (case-control & cohort studies) Experimental (RCTs, Field trial, community trial) 12  Made with Xodo PDF Reader and Editor Observational , Descriptive Studies The investigator allows nature to take its course, observes,measures & describes but does not interfere. Descriptive studies are essential in community medicine, for administrators and health policy makers, because they identify which groups of the population are more or less affected by health problems and inform decisions on the allocation of resources. 13  Made with Xodo PDF Reader and Editor Observational- Descriptive study Answers questions like: 1. Who? (PERSON) What are the characteristics of the population surveyed, (income, schooling, gender, age, and others)? 2. What? What is the condition studied?( needs a precise case definition, the forms of diagnosis, and its measures). 3. Why?. (FIND ASSOCIATIONS) Provide clues about the causes that can be elucidated in future research with more appropriate design 14  Made with Xodo PDF Reader and Editor Observational- Descriptive study Answers questions like: 4. When? The time indicates information and clues about the event in question. Was there a seasonal or cyclical variation? Did the distribution of the disease in question have an increasing or decreasing trend? Was it levelled off? 5. Where? (PLACE) How does the distribution of the event differ according to the regions of a country, state, or city? 15  Made with Xodo PDF Reader and Editor Observational- Descriptive study Descriptive studies use information routinely collected as census data, records of vital statistics on births and deaths, data from health services, or data that were specifically collected for registering the distribution of a given disease or health condition. Usually, observational studies are a first step towards the elucidation of health/ disease determinants 16  Made with Xodo PDF Reader and Editor Observational, Descriptive studies 1-case reports and case series A simple type of epidemiological study Relates to the reporting of one or more cases or even a series of cases. This is a detailed description of a certain number of manifestations of disease/condition/drug reaction or outcome of interventions Reporting in depth of the characteristics of interest, may suggest etiological hypotheses and represent an essential interface between clinical and epidemiological studies 17  Made with Xodo PDF Reader and Editor 18  Made with Xodo PDF Reader and Editor Observational, Descriptive studies 2- Cross-sectional studies (survey) In this type the researcher collects data from one or more populations at a single point in time. The researcher observe variables without influencing them. Cross-sectional studies measure the prevalence of disease/condition & are often called prevalence studies. 19  Made with Xodo PDF Reader and Editor Observational, Descriptive studies 2- Cross-sectional studies (survey) In a cross-sectional study the measurements of exposure and effect are made at the same time. The key question to be asked is whether the exposure precedes or follows the effect. It is not easy to assess the reasons for associations demonstrated in cross- sectional studies. When the aim is to describe the disease/condition in a given location, these studies are referred to as epidemiological surveys, a type of research that is often used in oral health. Cross-sectional studies may analytical when it aims to assess associations of interest, even if this association is not assessed in chronological order. 20  Made with Xodo PDF Reader and Editor 21  Made with Xodo PDF Reader and Editor Advantages of cross-sectional studies Relatively easy Economical to conduct Fast Don’t require follow up Are useful for investigating exposures of fixed characteristics in individuals, such as ethnicity, socioeconomic status, and blood group. In sudden outbreaks of diseases, cross-sectional study involving measurement of several exposures, is often the first step in an investigation into the cause. Such information may be useful in policy formulation, designing hypothesis- driven studies, and in interventions 22  Made with Xodo PDF Reader and Editor Advantages of cross-sectional studies Useful for the evaluation and planning of health services as Data from cross-sectional studies are helpful in assessing the health care needs of populations. Cross-sectional surveys of morbidity and the utilization of health services in different countries often give widely varying results, usually reflecting differences between populations, health states and needs. Attention must be given to the purposes of surveys; questionnaires must be well designed and the sample chosen must be appropriate. 23  Made with Xodo PDF Reader and Editor 24  Made with Xodo PDF Reader and Editor 25  Made with Xodo PDF Reader and Editor 26  Made with Xodo PDF Reader and Editor Results: Description of what was observed 27  Made with Xodo PDF Reader and Editor Disadvantages of cross-sectional studies Cross-sectional studies are not suited for etiologic research or causal analyses because they cannot identify incident disease Cross-sectional studies cannot establish temporal sequence of exposure of disease, and are subject to length bias 28  Made with Xodo PDF Reader and Editor Observational , Descriptive 3- Ecological studies Ecological studies, aggregated data studies, or georeferenced correlation studies They use information measured for population groups and not for individuals. Data aggregates are collected for populations from different geographical areas in the same time period. In ecological studies, the description and analysis are referred to the average exposure and the prevalence or rate of disease in the participating geopolitical units 29  Made with Xodo PDF Reader and Editor As an example of an ecological study, Screeby reported a strong correlation between the average DMFT index at 12 years and the supply of sugar in 47 countries. Both the exposure factor (sugar) and the outcome (caries) were measured at the population level, with data aggregated to the participating countries. 30  Made with Xodo PDF Reader and Editor Advantages of ecological studies They precisely explain the contextual effects on the prevalence of disease. Aggregated data studies have lower cost and analytical simplicity and are easy to conduct from an ethical standpoint. Ecological studies are beneficial for evaluating policies, programs, and interventions in health Useful for exposures that can only be measured in the population without correspondence at the individual level, for example, the Human Development Index of a region or municipality or relating health status to health care services 31  Made with Xodo PDF Reader and Editor Disadvantages of ecological studies The main limitation of the ecological study refers to the impossibility of inferring to the individual level as the results obtained at the population level (ecological fallacy). Another problem concerns the difficulty in controlling the possible confounding effect of factors not modelled at the level of aggregation of the study. 32  Made with Xodo PDF Reader and Editor Observational, Descriptive 4- Time series Time series studies constitute a unique form of aggregated data studies, in which aggregation is performed in a single geographic region of reference and in different periods. Time series analysis seeks to identify patterns of regularity in the variation of the variables under investigation. In epidemiological studies, the search for these regularity patterns addresses three preferential items: The temporal progression, involving the understanding of the forms of temporal variation of the measures of interest The concomitant variations of other population characteristics of interest The prediction of the most immediate future pattern of these variables. 33  Made with Xodo PDF Reader and Editor Classification of Epidemiological studies Epidemiological studies classification According to objective : Descriptive (case report/series, cross-sectional (survey), ecological, time series studies) Analytical (case-control & cohort studies,) According to methodology: Observational Descriptive (case report/series, cross-sectional (survey), ecological, time series studies) Analytical (case-control & cohort studies) Experimental (RCTs, Field trial, community trial) 34  Made with Xodo PDF Reader and Editor Thank you 35