ecological study.pdf

ECOLOGICAL study Presented by QAMAR ALSHAWISH  Introduction Ecological (also sometimes called as correlational) study focuses on the comparison of groups, rather than individuals, ecological studies are used to understand the relationship between outcome and exposure at a population...

ECOLOGICAL study Presented by QAMAR ALSHAWISH  Introduction Ecological (also sometimes called as correlational) study focuses on the comparison of groups, rather than individuals, ecological studies are used to understand the relationship between outcome and exposure at a population level, where 'population' represents a group of individuals w ith a shared characteristic such as geography, ethnicity, socio-economic status of employment individual-level data are missing on the joint distribution of variables w ithin groups. Variables in an ecologic analysis may be aggregate measures, environmental measures, or global measures.  Types of ecological studies 1-Geographical : this type of compares one geography w ith another by assessing the health of the population of each.Exposures for geographies may also be measured and included in analysis as well as other potential confounding variables such as demographic and socioeconomic information. 2-Longitudinal : A population is monitored to assess changes in disease over time. Again, confounding factors are often included in analysis. 3-Migration : Data of migrant populations are collected and analysed. The unit of interest in neither time or place , but population type.  TYPES OF MEASUREMENT Aggregate measures: Means or proportions in groups, derived from individuals in groups (e.g. % smokers in a country ) Environmental measures: E.g. air pollution level in a country Environmental measure has an analog at the individual level, but not easy to measure. Global measures: Attributes for groups or places for which there is no individual analog E.g. population density, type of healthcare system, political system in the country  Uses of ecological studied The purpose of the study is to monitor population health so that public health strategies may be developed and directed. The purpose of the study is to make large-scale comparisons, eg, comparisons between countries. The purpose of the study is to study the relationship between population-level exposure to risk factors and disease, or in order to look at the contextual effect of risk factors on the population  Limitations of ecologic studies First Second Third fourth an association consideration may the association may migration of people between exposure be related to a between regions be the use of and outcome at the third factor which differing w ith different group level may not in turn is related to definitions for exposure levels be true at the both the exposure may also introduce exposure, outcome individual level ( a and the outcome , an error. or both in phenomenon also the so-called different referred to as “confounding”. “ecological fallacy”). populations  An ecological study correlated per capita alcohol consumption to death rates from coronary heart disease (CHD) in different countries, and it appeared that there was a fairly striking negative correlation as shown in the graph below  summary In contemporary Ecological Unit of It is The epidemiology , the study study is usually result “ecologic fallacy” is a the conducted is reflects the difficult failure of the Aggregate as the convenient, data first step to interpret investigator to recognize the need cheap not in study because for biologic and simple individual for of inference and thus for study level. research. confounding individual-level and bias. data Thank you!