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Epidemiology: Study of the distribution and determinants of health-related states or events in a specific population and the application of results to control health problems.
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Epidemiology is the study and analysis of the distribution who, when, and where , patterns and determinants of health and disease conditions in defined populations. It is a cornerstone of public health , and shapes policy decisions and evidence-based practice by identifying risk factors for disease and targets for preventive healthcare.
Epidemiologists help with study design, collection, and statistical analysis of data, amend interpretation and dissemination of results including peer review and occasional systematic review. Epidemiology has helped develop methodology used in clinical research , public health studies, and, to a lesser extent, basic research in the biological sciences.
Major areas of epidemiological study include disease causation, transmission , outbreak investigation, disease surveillance , environmental epidemiology , forensic epidemiology , occupational epidemiology , screening , biomonitoring , and comparisons of treatment effects such as in clinical trials.
Epidemiologists rely on other scientific disciplines like biology to better understand disease processes, statistics to make efficient use of the data and draw appropriate conclusions, social sciences to better understand proximate and distal causes, and engineering for exposure assessment.
However, the term is widely used in studies of zoological populations veterinary epidemiology , although the term " epizoology " is available, and it has also been applied to studies of plant populations botanical or plant disease epidemiology.
The distinction between "epidemic" and "endemic" was first drawn by Hippocrates ,  to distinguish between diseases that are "visited upon" a population epidemic from those that "reside within" a population endemic. The term epidemiology is now widely applied to cover the description and causation of not only epidemic disease, but of disease in general, and even many non-disease, health-related conditions, such as high blood pressure, depression and obesity.
Therefore, this epidemiology is based upon how the pattern of the disease causes change in the function of human beings. The Greek physician Hippocrates , known as the father of medicine ,   sought a logic to sickness; he is the first person known to have examined the relationships between the occurrence of disease and environmental influences.
The cure to the sickness was to remove or add the humor in question to balance the body. This belief led to the application of bloodletting and dieting in medicine. In the middle of the 16th century, a doctor from Verona named Girolamo Fracastoro was the first to propose a theory that these very small, unseeable, particles that cause disease were alive. They were considered to be able to spread by air, multiply by themselves and to be destroyable by fire.
In this way he refuted Galen 's miasma theory poison gas in sick people. In he wrote a book De contagione et contagiosis morbis , in which he was the first to promote personal and environmental hygiene to prevent disease. The development of a sufficiently powerful microscope by Antonie van Leeuwenhoek in provided visual evidence of living particles consistent with a germ theory of disease. A physician ahead of his time, Quinto Tiberio Angelerio, managed the plague in the town of Alghero, Sardinia.
He was fresh from Sicily, which had endured a plague epidemic of its own in Some of the rules he instituted, several as unpopular then as they are today, included lockdowns, physical distancing, washing groceries and textiles, restricting shopping to one person per household, quarantines, health passports, and others.
Another pioneer, Thomas Sydenham — , was the first to distinguish the fevers of Londoners in the later s. His theories on cures of fevers met with much resistance from traditional physicians at the time. He was not able to find the initial cause of the smallpox fever he researched and treated.
John Graunt , a haberdasher and amateur statistician, published Natural and Political Observations In it, he analysed the mortality rolls in London before the Great Plague , presented one of the first life tables , and reported time trends for many diseases, new and old. He provided statistical evidence for many theories on disease, and also refuted some widespread ideas on them. John Snow is famous for his investigations into the causes of the 19th-century cholera epidemics, and is also known as the father of modern epidemiology.
His identification of the Broad Street pump as the cause of the Soho epidemic is considered the classic example of epidemiology. Snow used chlorine in an attempt to clean the water and removed the handle; this ended the outbreak. This has been perceived as a major event in the history of public health and regarded as the founding event of the science of epidemiology, having helped shape public health policies around the world.
This was used to rationalize high rates of infection in impoverished areas instead of addressing the underlying issues of poor nutrition and sanitation, and was proven false by his work. Other pioneers include Danish physician Peter Anton Schleisner , who in related his work on the prevention of the epidemic of neonatal tetanus on the Vestmanna Islands in Iceland.
His findings were published in , but his work was ill-received by his colleagues, who discontinued the procedure. Disinfection did not become widely practiced until British surgeon Joseph Lister 'discovered' antiseptics in in light of the work of Louis Pasteur. Another breakthrough was the publication of the results of a British Doctors Study , led by Richard Doll and Austin Bradford Hill , which lent very strong statistical support to the link between tobacco smoking and lung cancer.
In the late 20th century, with the advancement of biomedical sciences, a number of molecular markers in blood, other biospecimens and environment were identified as predictors of development or risk of a certain disease. Epidemiology research to examine the relationship between these biomarkers analyzed at the molecular level and disease was broadly named " molecular epidemiology ". Specifically, " genetic epidemiology " has been used for epidemiology of germline genetic variation and disease.
Genetic variation is typically determined using DNA from peripheral blood leukocytes. Since the s, genome-wide association studies GWAS have been commonly performed to identify genetic risk factors for many diseases and health conditions.
While most molecular epidemiology studies are still using conventional disease diagnosis and classification systems, it is increasingly recognized that disease progression represents inherently heterogeneous processes differing from person to person. Studies to examine the relationship between an exposure and molecular pathologic signature of disease particularly cancer became increasingly common throughout the s.
However, the use of molecular pathology in epidemiology posed unique challenges, including lack of research guidelines and standardized statistical methodologies, and paucity of interdisciplinary experts and training programs. To resolve these issues and advance population health science in the era of molecular precision medicine , " molecular pathology " and "epidemiology" was integrated to create a new interdisciplinary field of " molecular pathological epidemiology " MPE ,   defined as "epidemiology of molecular pathology and heterogeneity of disease".
In MPE, investigators analyze the relationships between A environmental, dietary, lifestyle and genetic factors; B alterations in cellular or extracellular molecules; and C evolution and progression of disease.
A better understanding of heterogeneity of disease pathogenesis will further contribute to elucidate etiologies of disease. The MPE approach can be applied to not only neoplastic diseases but also non-neoplastic diseases. By it was recognized that many pathogens' evolution is rapid enough to be highly relevant to epidemiology, and that therefore much could be gained from an interdisciplinary approach to infectious disease integrating epidemiology and molecular evolution to "inform control strategies, or even patient treatment.
Modern epidemiological studies can use advanced statistics and machine learning to create predictive models as well as to define treatment effects.
Epidemiologists employ a range of study designs from the observational to experimental and generally categorized as descriptive involving the assessment of data covering time, place, and person , analytic aiming to further examine known associations or hypothesized relationships , and experimental a term often equated with clinical or community trials of treatments and other interventions.
In observational studies, nature is allowed to "take its course," as epidemiologists observe from the sidelines. Conversely, in experimental studies, the epidemiologist is the one in control of all of the factors entering a certain case study. The identification of causal relationships between these exposures and outcomes is an important aspect of epidemiology. Modern epidemiologists use informatics as a tool. Observational studies have two components, descriptive and analytical.
Descriptive observations pertain to the "who, what, where and when of health-related state occurrence". The term 'epidemiologic triad' is used to describe the intersection of Host , Agent , and Environment in analyzing an outbreak.
Case-series may refer to the qualitative study of the experience of a single patient, or small group of patients with a similar diagnosis, or to a statistical factor with the potential to produce illness with periods when they are unexposed.
The former type of study is purely descriptive and cannot be used to make inferences about the general population of patients with that disease. These types of studies, in which an astute clinician identifies an unusual feature of a disease or a patient's history, may lead to a formulation of a new hypothesis. Using the data from the series, analytic studies could be done to investigate possible causal factors. These can include case-control studies or prospective studies. A case-control study would involve matching comparable controls without the disease to the cases in the series.
A prospective study would involve following the case series over time to evaluate the disease's natural history. The latter type, more formally described as self-controlled case-series studies, divide individual patient follow-up time into exposed and unexposed periods and use fixed-effects Poisson regression processes to compare the incidence rate of a given outcome between exposed and unexposed periods.
This technique has been extensively used in the study of adverse reactions to vaccination and has been shown in some circumstances to provide statistical power comparable to that available in cohort studies. Case-control studies select subjects based on their disease status. It is a retrospective study. A group of individuals that are disease positive the "case" group is compared with a group of disease negative individuals the "control" group.
The control group should ideally come from the same population that gave rise to the cases. The case-control study looks back through time at potential exposures that both groups cases and controls may have encountered. If the OR is significantly greater than 1, then the conclusion is "those with the disease are more likely to have been exposed," whereas if it is close to 1 then the exposure and disease are not likely associated. If the OR is far less than one, then this suggests that the exposure is a protective factor in the causation of the disease.
Case-control studies are usually faster and more cost-effective than cohort studies but are sensitive to bias such as recall bias and selection bias.
The main challenge is to identify the appropriate control group; the distribution of exposure among the control group should be representative of the distribution in the population that gave rise to the cases. This can be achieved by drawing a random sample from the original population at risk. This has as a consequence that the control group can contain people with the disease under study when the disease has a high attack rate in a population. As the odds ratio approached 1, approaches 0; rendering case-control studies all but useless for low odds ratios.
For instance, for an odds ratio of 1. Cohort studies select subjects based on their exposure status. The study subjects should be at risk of the outcome under investigation at the beginning of the cohort study; this usually means that they should be disease free when the cohort study starts.
The cohort is followed through time to assess their later outcome status. An example of a cohort study would be the investigation of a cohort of smokers and non-smokers over time to estimate the incidence of lung cancer. As with the OR, a RR greater than 1 shows association, where the conclusion can be read "those with the exposure were more likely to develop disease. Prospective studies have many benefits over case control studies. The RR is a more powerful effect measure than the OR, as the OR is just an estimation of the RR, since true incidence cannot be calculated in a case control study where subjects are selected based on disease status.
Temporality can be established in a prospective study, and confounders are more easily controlled for. However, they are more costly, and there is a greater chance of losing subjects to follow-up based on the long time period over which the cohort is followed.
Although epidemiology is sometimes viewed as a collection of statistical tools used to elucidate the associations of exposures to health outcomes, a deeper understanding of this science is that of discovering causal relationships.
For epidemiologists, the key is in the term inference. Correlation, or at least association between two variables, is a necessary but not sufficient criterion for inference that one variable causes the other. Epidemiologists use gathered data and a broad range of biomedical and psychosocial theories in an iterative way to generate or expand theory, to test hypotheses, and to make educated, informed assertions about which relationships are causal, and about exactly how they are causal.
Epidemiologists emphasize that the " one cause — one effect " understanding is a simplistic mis-belief. If a necessary condition can be identified and controlled e. One tool regularly used to conceptualize the multicausality associated with disease is the causal pie model.
In , Austin Bradford Hill proposed a series of considerations to help assess evidence of causation,  which have come to be commonly known as the " Bradford Hill criteria ". In contrast to the explicit intentions of their author, Hill's considerations are now sometimes taught as a checklist to be implemented for assessing causality. Epidemiological studies can only go to prove that an agent could have caused, but not that it did cause, an effect in any particular case:.
Epidemiology Quizlet Midterm
You will learn about commonly used epidemiological measurements to describe the occurrence of disease. This section covers:. The essence of epidemiology is to measure disease occurrence and make comparisons between population groups. The current section introduces the commonly used measures that help our understanding of the distribution of disease in a given population. A principal role of epidemiology is to describe and explain differences in the distribution of disease or other health outcomes of interest between populations.
The researchers decide to recruit patients from a pulmonary ward to try answering the question. In the ward, 12 of the admitted patients have lung cancer and
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Epidemiology is the study and analysis of the distribution who, when, and where , patterns and determinants of health and disease conditions in defined populations. It is a cornerstone of public health , and shapes policy decisions and evidence-based practice by identifying risk factors for disease and targets for preventive healthcare. Epidemiologists help with study design, collection, and statistical analysis of data, amend interpretation and dissemination of results including peer review and occasional systematic review. Epidemiology has helped develop methodology used in clinical research , public health studies, and, to a lesser extent, basic research in the biological sciences.
All of the following are true of odds ratio except: A. Dewi Suryani, M. Note: Questions can be multiple choice indicate the one correct answer or multiple response squares indicate all answers that are correct. To calculate the mean, we just add up all 7 values, and divide by 7. Arachnoid, Pia, Blood C.
Written and peer-reviewed by physicians—but use at your own risk. Read our disclaimer. Classical epidemiology is the study of the distribution and determinants of disease in populations. There are two main types of epidemiological studies : observational and experimental.
A Ask a question, analyze results, make a hypothesis, test the hypothesis, draw conclusions, communicate results. Maria Sevoyan joined the Department of Epidemiology and Biostatistics and spent the next several years amassing knowledge and experience in new epidemiology methods, analytical skills and techniques to use in clinical and public health research.
Grading is based equally on homework including the problem-writing assignment, which counts as 1 homework and a take-home final exam. It often helps to form groups before an exam and have each member review specific chapters or topics covered in the class. Doctoral student completes epidemiology degree to improve health in Armenia.
Now that you have read Lesson 1 and have completed the exercises, you should be ready to take the self-assessment quiz. This quiz is designed to help you assess how well you have learned the content of this lesson. You may refer to the lesson text whenever you are unsure of the answer.