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Epidemiology
The document discusses the principles, goals, and methods of epidemiology, defining it as the study of health-related states or events in specified populations. It outlines the distribution, determinants, and applications of epidemiology, emphasizing its role in understanding disease causes and improving community health. Various study designs, including observational and experimental studies, are described to illustrate epidemiological research methods.
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Introduces epidemiology's definition, etymology, and significance in health studies.
Discusses distribution, frequency, and determinants of health events, emphasizing community health focus.
Describes four eras of epidemiology: sanitary, infectious diseases, chronic disease, and eco-epidemiology.
Outlines the aims: understanding disease causes, service planning, and improving health outcomes.
Focuses on minimizing health complications and enhancing community well-being by defining disease history.
Explains the interdisciplinary approach of epidemiology encompassing clinical, biological, and social aspects.
Categorizes the uses of epidemiology in health status assessments and disease etiology investigations.
Categorizes epidemiological studies into observational and experimental types, explaining their significance.
Defines descriptive epidemiology, focusing on health features distribution and initial investigation phases.
Introduces analytical epidemiology, highlighting case-control studies and their methodological features.
Details on cohort studies as analytical methods, focusing on prospective and retrospective study types.
Discusses experimental epidemiology and randomized controlled trials to test disease causation and interventions.
Summarizes that epidemiology examines population health through various study designs for precise analysis.
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Epidemiology
- 1. EPIDEMIOLOGY Harsh Rastogi PhD student CommunityOphthalmology Advanced Eye Centre PGIMER, Chandigarh
- 2. INTRODUCTION • The termepidemiology is derived from the Greek word epidemic. • Epi – among, upon • Demos- people • Logos – scientific study
- 3. DEFINITION • The widelyaccepted definition of epidemiology is: “The study of the distribution and determinants of health related states or events in specified population and the application of the study to control of health problems.” (J. M. Last 1988)
- 4. PRINCIPLES OF EPIDEMIOLOGY DISTRIBUTION: Epidemiologystudies the frequency and pattern of health events in a given population. FREQUENCY: Epidemiology is measurement of frequency of disease, disability or death. Thus the basic measure of disease frequency is rates and ratio.
- 5. PRINCIPLES (CONT.) PATTERN: Refersto the occurrence of health related events by time, place and person. Time- It may be annual, seasonal, weekly, daily, hourly, or any other breakdown of time that may influence disease or injury occurrence. Place- This includes the variations found in geographic region, urban and rural differences, and location of work sites. Person- It includes demographic factors such as age, sex, marital status, socioeconomic status, behaviors and environmental exposures.
- 6. PRINCIPLES (CONT.) DETERMINANTS: Determinants areany factor that decides the change in an event, characteristics, or other definable entity that contributes to the development of some illness. HEALTH RELATED STATES OR EVENTS: The term health related states or events may be seen as anything that affects the well being of a population.
- 7. PRINCIPLES (CONT.) SPECIFIED POPULATIONS: Thephysician in the hospital shows interest on the health of an individual whereas the epidemiologist is concerned about the health of the people in a community or population. The physician’s focus is the individual patient; the epidemiologist’s “patient” is the community. The clinician usually focuses on curing and caring for individual, the epidemiologist focuses on identifying the exposure or source that caused the illness.
- 8. PRINCIPLE (CONT.) APPLICATION: The significantfeature of epidemiology is application of the gained knowledge for community based practice.
- 9. CONCEPT OF EPIDEMIOLOGY Contemporaryepidemiology can be divided into four diverse eras, each based on fundamental casual thinking. They include: • Sanitary statistics epidemiology: Theory believed that the disease were caused by poisonous and malodour elements released from decomposed organic matters. • Infectious disease epidemiology: Disease etiology is a complex phenomenon involving host-infectious agent connections.
- 10. CONCEPT (CONT.) • Chronicdisease epidemiology: Antibiotics and chemotherapy were introduced as preventative and curative treatments for major infectious diseases following the identification of their causative agents, but non-communicable diseases with complex etiologies continue to pose a significant burden. • Eco epidemiology: In relation to the environment, global health patterns, illness transmission routes, and disease occurrence are undergoing rapid change.
- 11. GOALS OF EPIDEMIOLOGY •To understand the cause of disease variance and apply this knowledge to improve population and individual health. • To prevent and control disease, regulate health and health care planning, and improve individual health care. • The ultimate objective is to characterize the magnitude and nature of people's health problems, discover strategies for preventing disease, and improve the population's health.
- 12. AIMS OF EPIDEMIOLOGY •According to the International Association for Epidemiology (IEA), epidemiology has three primary objectives: 1. To describe the distribution and magnitude of health and disease challenges in the human population. 2. To uncover etiological factors in disease pathogenesis. 3. Provide the data necessary for the planning, implementation, and evaluation of services for the prevention, control, and treatment of disease, as well as the establishment of service priorities.
- 13. ULTIMATE AIM OFEPIDEMIOLOGY Epidemiology's ultimate goal is to lead to effective action: a. To eliminate or minimize health complications or their consequences b. To enhance the health and well-being of the entire community.
- 14. PURPOSE OF EPIDEMIOLOGY •Define and interpret the natural history of diseases. • Health status of the population is described. • Identifying disease-causing factors. • Effectiveness of intervention is evaluated
- 15. SCOPE OF EPIDEMIOLOGY •Clinical, biological, social, and ecological disciplines are combined in epidemiology. • To make a diagnosis, the first step in epidemiological study, epidemiology requires clinical practice and the sciences. • Formally, Epidemiology demonstrated an interest in studying and managing epidemics of communicable diseases. • Recently, epidemiology has been used to analyze communicable endemic diseases and noncommunicable diseases. • Now, epidemiology is a science applicable to all diseases and other health-related occurrences.
- 16. USES OF EPIDEMIOLOGY Accordingto Morris J N the following are the applications of epidemiology. Morris J N categorized uses into: • Uses associated with health status and health services • To investigate the demographic's health's background • To assess the community's health status • To study the medical services
- 17. USES (CONT.) Applications relatedto disease etiology: • To assess individual risks • To detect syndromes • To characterize the clinical manifestations of chronic conditions • To investigate causes of health and disease
- 18.
- 19. Types of Epidemiologicalstudies Non- experimental/Observational Studies Population based Descriptive (Health Survey) Analytic (Ecological Study) Individual based Descriptive/ Case reports/ Case series/ Analytic Cross-sectional studies/Prevalence study Case control study/Case- reference Cohort study/Follow-up study Experimental/In terventional Studies Randomized Control Trial/Clinical Trial Non-randomized Quasi experimental/Field trial/ Community trial
- 20. INTRODUCTION Epidemiological studies canbe classified as: 1.Observational studies • Descriptive studies or Health survey • Analytical studies • Ecological or co relational • Cross sectional or prevalence • Case control or case reference • Cohort or follow up
- 21. INTRODUCTION (CONT.) 2. Experimentalor interventional studies: • Randomized control trial or clinical trial • Quasi-experimental • Field trials • Community trials
- 22. DESCRIPTIVE EPIDEMIOLOGY • Descriptivestudies are frequently the initial phase of an epidemiological investigation. • These studies are concerned with observing the distribution of disease or health- related features in human populations and finding the variables that appear to be associated with the disease in question.
- 23. DESCRIPTIVE EPIDEMIOLOGY (CONT.) Essentially,descriptive studies pose the questions: • When does the disease manifest? (Time distribution) • Where is it taking place? (Place distribution) • Who is infected with the disease?(Person distribution) Epidemiology Time Place People
- 24. DESCRIPTIVE EPIDEMIOLOGY (CONT.) Thevarious procedures involved in descriptive studies are as follows: • Specify the study population. • Define the disease being studied. • Time, place, and person are used to describe a disease. • Disease characterization • Using known indices for comparison. • Etiology hypothesis formulation.
- 25. DESCRIPTIVE EPIDEMIOLOGY (CONT.) Specifythe study population Define the disease being studied Time, place, and person are used to describe a disease Disease characterization Using known indices for comparison Etiology hypothesis formulation The various procedures involved in descriptive studies are as follows:
- 26. DESCRIPTIVE EPIDEMIOLOGY (CONT.) •In terms of mortality and morbidity rate, provide information regarding the disease burden and disease problem in the community. • Provide a clue to the etiology of the disease and aid in the creation of an etiological hypothesis. • Provide background information for service planning, evaluation, organization, prevention, and treatment. • They contribute to research by describing variation in disease occurrence by time, place, and person.
- 27. ANALYTICAL EPIDEMIOLOGY • Itis the second major type of epidemiological studies. • In the analytical studies the subject of interest is the individual within the population. • The object is not formulated but to test hypothesis. • It includes two distinct types of observational studies • Case control • Cohort study
- 28. CASE CONTROL STUDY •It is often called retrospective study, are common first approach to test casual hypothesis. • In recent years, the case control approach has emerged as a permanent method of epidemiological investigation. • A case control study involves two populations- cases and controls. • In case control studies the unit is the individual rather than the group. • The focus is on a disease or some other health problems that has already developed.
- 29. CASE CONTROL STUDY(CONT.) The case control method has three distinct features: • Both exposure and outcome( disease have occurred before start of the study) • The study proceeds backward from effect to cause. • It uses the control or comparison group to support or refute an inference.
- 30. CASE CONTROL STUDY(CONT.) There are four basic steps in conducting a case control study: Selection of cases and controls Matching Measurement of exposure, and Analysis and interpretation.
- 31. DESIGN OF CASECONTROL STUDY Direction of inquiry Time Population Cases( people with diseases) Exposed Not Exposed Control( people without diseases) Exposed Not Exposed
- 32. COHORT STUDY • Cohortstudy is another type of analytical (observational study) which is usually undertaken to obtain additional evidence to refute or support the existence of an association between suspected cause and disease. • This study is also known as prospective study, longitudinal study, incidence study, and forward looking study.
- 33. COHORT STUDY (CONT.) Thedistinguishing features of cohort studies are: • The cohorts are identified prior to the appearance of the disease under investigation. • The study groups, so defined, are observed over a period of time to determine the frequency of disease among them. • The study proceeds forward from cause to effect.
- 34. COHORT STUDY (CONT.) Thethree types of cohort studies are as follows: Prospective cohort study Retrospective cohort study A combination of both
- 35. COHORT STUDY (CONT.) Theelements of cohort study are: Selection of study subject Obtaining data on exposure Selection of comparison group Follow up and Analysis
- 36. EXPERIMENTAL EPIDEMIOLOGY • Inthe 1920s, “experimental epidemiology” meant the study of epidemics among the colonies of experimental animals such as rats and mice. • In modern usage, experimental epidemiology is often equated with RANDOMISED CONTROLLED TRIALS.
- 37. EXPERIMENTAL EPIDEMIOLOGY (CONT.) •Experimental studies involves some action, intervention or manipulation such as deliberate application or withdrawal. • The suspected cause or changing one variable in the causative chain in the experimental group while making no change in the control group, and observing and comparing the outcome of the experiment in both the groups. • They may be conducted in animals or human beings.
- 38. AIMS OF EXPERIMENTALSTUDIES • To provide scientific proof of etiological factors which may permit the modification or control of those diseases. • To provide a method of measuring the effectiveness and efficiency of health services for the prevention, control and treatment of disease and improve the health of the community.
- 39. RANDOMIZED CONTROL TRIAL •The basic step in conducting a RCT include the following: Drawing up a protocol Selecting reference and experimental populations Randomization Manipulation or intervention Follow up Assessment of outcomes
- 41. CONCLUSION • In conclusion,epidemiology is the study of the health and disease of an entire population, not a single individual. • Epidemiology employs a variety of study designs to analyze a specific population. • This design facilitates precise population studies.
- 42.