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Fundamentals and Study Design of Epidemiology Slide 1 Fundamentals and Study Design of Epidemiology Slide 2 Fundamentals and Study Design of Epidemiology Slide 3 Fundamentals and Study Design of Epidemiology Slide 4 Fundamentals and Study Design of Epidemiology Slide 5 Fundamentals and Study Design of Epidemiology Slide 6 Fundamentals and Study Design of Epidemiology Slide 7 Fundamentals and Study Design of Epidemiology Slide 8 Fundamentals and Study Design of Epidemiology Slide 9 Fundamentals and Study Design of Epidemiology Slide 10 Fundamentals and Study Design of Epidemiology Slide 11 Fundamentals and Study Design of Epidemiology Slide 12 Fundamentals and Study Design of Epidemiology Slide 13 Fundamentals and Study Design of Epidemiology Slide 14 Fundamentals and Study Design of Epidemiology Slide 15 Fundamentals and Study Design of Epidemiology Slide 16 Fundamentals and Study Design of Epidemiology Slide 17 Fundamentals and Study Design of Epidemiology Slide 18 Fundamentals and Study Design of Epidemiology Slide 19 Fundamentals and Study Design of Epidemiology Slide 20 Fundamentals and Study Design of Epidemiology Slide 21 Fundamentals and Study Design of Epidemiology Slide 22 Fundamentals and Study Design of Epidemiology Slide 23 Fundamentals and Study Design of Epidemiology Slide 24 Fundamentals and Study Design of Epidemiology Slide 25 Fundamentals and Study Design of Epidemiology Slide 26 Fundamentals and Study Design of Epidemiology Slide 27 Fundamentals and Study Design of Epidemiology Slide 28 Fundamentals and Study Design of Epidemiology Slide 29 Fundamentals and Study Design of Epidemiology Slide 30 Fundamentals and Study Design of Epidemiology Slide 31 Fundamentals and Study Design of Epidemiology Slide 32 Fundamentals and Study Design of Epidemiology Slide 33 Fundamentals and Study Design of Epidemiology Slide 34 Fundamentals and Study Design of Epidemiology Slide 35 Fundamentals and Study Design of Epidemiology Slide 36 Fundamentals and Study Design of Epidemiology Slide 37 Fundamentals and Study Design of Epidemiology Slide 38 Fundamentals and Study Design of Epidemiology Slide 39 Fundamentals and Study Design of Epidemiology Slide 40 Fundamentals and Study Design of Epidemiology Slide 41 Fundamentals and Study Design of Epidemiology Slide 42 Fundamentals and Study Design of Epidemiology Slide 43 Fundamentals and Study Design of Epidemiology Slide 44 Fundamentals and Study Design of Epidemiology Slide 45 Fundamentals and Study Design of Epidemiology Slide 46 Fundamentals and Study Design of Epidemiology Slide 47 Fundamentals and Study Design of Epidemiology Slide 48 Fundamentals and Study Design of Epidemiology Slide 49 Fundamentals and Study Design of Epidemiology Slide 50 Fundamentals and Study Design of Epidemiology Slide 51 Fundamentals and Study Design of Epidemiology Slide 52
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Fundamentals and Study Design of Epidemiology

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Fundamentals, Epidemiological methods and Study Design and conduct of Clinical Trials in Epidemiological set up.

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Fundamentals and Study Design of Epidemiology

  1. 1. Fundamentals of Epidemiology, Epidemiologic Methods, Design and Conduct of Clinical Trials Faraza Javed Ph.D Pharmacology
  2. 2. 2 Introduction The term epidemiology is derived from the Greek word epidemic. Epi means-Among, upon, Demos means study population or people and Logos means scientific study. So It is the scientific study of the disease pattern in human population. In broad sense, it is the study of effects of multiple factors on human health. It is multidisciplinary subject involving those of the physician, Biologists, Public Health experts, Health educators etc.
  3. 3. 3 The science of the mass phenomena of infectious diseases or the natural history of infectious diseases. (Frost 1927) The science of infective diseases, their prime causes, propagation and prevention. (Stallbrass 1931)
  4. 4. 4 The widely accepted 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)
  5. 5. Aims of Epidemiology According to the International Epidemiological Association (IEA) Epidemiology has three main aims. To describe and analyze diseases occurrence and distribution in human populations; To identify etiological factors in the pathogenesis of diseases; To provide the data essential to the planning, implementation and evaluation of services for the prevention, control and treatment of diseases and to the setting up of priorities among those services.
  6. 6. 6 Components of Epidemiology Disease frequency:  The core characteristics of epidemiology are to measure the frequency of diseases, disability or death in a specified population. it is always as the rate, ratio and proportion.  Much of the subject of epidemiology are matter of measurement of diseases and health related events falls in the domain of biostatistics, which is a basic tool of epidemiology. This helps in development of strategies for prevention or control of health related problems.
  7. 7. 7 Distribution of Diseases:  Health events occur in pattern in community and this pattern varies from community to community.  Also health events or diseases condition affect population at various age groups, different genders, different subgroups of population.  Distributions of events are based on time, place, and person. We can analyze whether any increases or decreases occur for a particular condition. Epidemiology addresses itself to a study of these variations or patterns, which may suggest or lead to measure to control or prevent the diseases. An important outcome of this study is formulation of etiological hypothesis.
  8. 8. 8 Determinants of Diseases:  Epidemiology helps in identifying the causative agent or the risk/predisposing factors of diseases.  This is one of the real uses of epidemiology. Understanding the factors leading to any programs for the control of those diseases.
  9. 9. How to study the disease in the community? Clinical Method: Studied subject is a patient (individual person) and decision on his/her treatment requires a clinical diagnosis (based on the history, examination, laboratory tests, etc.).
  10. 10. Epidemiological Method: Epidemiology studies not only an individual, but also a whole population. Community diagnosis is essential and can be expressed in terms of rates.
  11. 11. Basic Measurement  Prevalence Rate  Incidence rate  Case fatality rate  Mortality rates(age specific/cause specific)  Attack rate 11
  12. 12. Prevalence vs. Incidence Prevalence: frequency of existing cases Incidence: frequency of new cases New cases are called incident cases. Existing cases are called prevalent cases. 12
  13. 13. PREVALENCE RATE No. of people with disease at specified time/No. of people in Population at risk at specified time x 1000 Prevalence rate is often used to measure the occurrence of chronic (long lasting) diseases or diseases with gradual onset (such as diabetes, sclerosis multiplex, tuberculosis etc.)
  14. 14. Ex: The Percentage of under five children with acute malnutrition in Africa in March 2008
  15. 15. INCIDENCE RATE Incidence Rate is defined as the no. of NEW cases occurring in a defined population during a specified time period. No. of new cases of specific disease during a given time period/ Population at risk during that period X 1000 Incidence rate is often used to measure the occurrence of acute (short-term) diseases or diseases with exactly defined onset (such as acute intestinal diseases, poisonings, car accidents, strokes, etc.) 15
  16. 16. For example , if there had been 500 new cases of an illness in a population of 30,000 in a year, the incidence rate would be : 500/30000 x 1000 = 16.7  Incidence rate refers to only new cases.
  17. 17. 17
  18. 18. ATTACK RATE The attack rate, or case rate, refers to the cumulative incidence of infection over a period of time. This is typically used during an epidemic. The time period may not be indicated, but would typically refer to the period of the outbreak.
  19. 19. Ex: Outbreak of cholera in country X in March 1999 Number of cases = 490, Population at risk = 18,600 Then the Attack rate = 2.6%
  20. 20. CASE FATALITY RATE Measure of the severity of a disease which defined as the proportion of cases of a specified disease or condition which are fatal within a specified time = no. of death from a disease in a specified period no. of diagnosed cases of disease in same period X 100 20
  21. 21. The proportion of people with a specified condition who die within a specified time. The time frame is typically the period during which the patient is sick from the disease. This works for an infectious disease but can be problematic for a chronic disease like a cancer that may remit for a period and then prove fatal after a recurrence. In such instances we tend to speak of mortality or survival rates rather than case fatality.
  22. 22. MORTALITY RATE The number of deaths per thousand population per year: in effect, the incidence of death in a population. It can refer to all causes of death, or can be a cause-specific mortality rate.
  23. 23. It expresses the no. of death due to a particular cause (or in a specific age group) per 100 (or 1000) total deaths No. of deaths from the specific disease in a year x 100 Total deaths from all causes in that year
  24. 24. EPIDEMIOLOGICAL STUDIES When we need to obtain more precise or detailed data, it may be necessary to undertake a special survey. Planning of the study: Definition of the aim of the study and type of the study. Determination of the studied population (target population)-to exactly define the attributes of individuals belonging to this population (including and excluding criteria)
  25. 25.  Case definition – to define a tool for discrimination positive and negative cases. This tool (method) should be cheap, simple and readily available.
  26. 26. 26 Epidemiologic Study Designs
  27. 27. 27 Study Design Study design is the arrangement of conditions for the collection and analysis of data to provide the most accurate answer to a question in the most economical way.
  28. 28. 28 Types 1. Cross-sectional studies 2. Case-control studies 3. Cohort studies 4. Experimental studies
  29. 29. 29 Cross-sectional Studies  In this study design information about the status of an individual with respect to presence/absence of exposure and diseased is assessed at a point in time.  Cross-sectional studies are useful to generate a hypothesis rather that to test it  For factors that remain unaltered overtime (e.g. gender, race, blood group) it can produce a valid association
  30. 30. 30 Cross-Sectional…  Comparison groups are formed after data collection  The object of comparison are prevalence of exposure or disease  Groups are compared either by exposure or disease status  Cross-sectional studies are also called prevalence studies
  31. 31. 31 Cross-sectional… Types of cross-sectional studies 1. Single cross-sectional studies Determine single proportion/mean in a single population at a time 2. Comparative cross-sectional studies Determine two proportions/means in two populations at a time
  32. 32. 32 Cross-sectional… Advantages of cross-sectional studies  Less time consuming  Less expensive  Provides more information  Describes well  Generates hypothesis
  33. 33. 33 Cross-sectional… Limitations of cross-sectional studies  Antecedent-consequence uncertainty “Chicken or egg dilemma”  Data dredging leading to inappropriate comparison  More vulnerable to bias
  34. 34. 34 Case-Control Studies  Subjects are selected with respect to the presence (cases) or absence (controls) of disease, and then inquiries are made about past exposure  We compare diseased (cases) and non-diseased (controls) to find out the level of exposure  Exposure status is traced backward in time
  35. 35. 35 Case-control… Steps in conducting case-control studies: Define who is a case Establish strict diagnostic criteria All who fulfil the criteria will be “case population Those who don’t fulfil will be “control population”
  36. 36. Individuals are divided according to presence of the disease: studied group (disease present, e.g. lung cancer) and control group (disease absent, e.g. without lung cancer). Occurrence of suspected risk factor in history is compared in both groups (e.g. proportion of smokers) (studies focused from consequence to cause)
  37. 37. 37 Case-control… Advantages of case-control studies  Optimal for evaluation of rare diseases  Examines multiple factors of a single disease  Quick and inexpensive  Relatively simple to carry out  Guarantee the number of people with disease
  38. 38. 38 Cohort studies Subjects are selected by exposure and followed to see development of disease Two types of cohort studies 1. Prospective (classical)  Outcome hasn’t occurred at the beginning of the study  It is the commonest and more reliable
  39. 39. 39 Cohort… 2. Retrospective (Historical)  Both exposure and disease has occurred before the beginning of the study  Faster and more economical  Data usually incomplete and in accurate
  40. 40. 40 Cohort… Steps in conducting cohort studies  Define exposure  Select exposed group  Select non-exposed group  Follow and collect data on outcome  Compare outcome b/w exposed & non-exposed
  41. 41. 41 Cohort… Advantages of cohort studies  Valuable when exposure is rare  Examines multiple effects of a single exposures  Allow direct measurement of risk
  42. 42. 42 Cohort… Limitations of cohort studies  Expensive  Time-consuming  Loss to follow-up creates a problem
  43. 43. 43 Experimental studies Individuals are allocated in to treatment and control groups by the investigator. If properly done, experimental studies can produce high quality data. They are the gold standard study design. They included studied group (intervention, e.g. vaccinated children), control group (without intervention, e.g. non-vaccinated children)
  44. 44. 44 Experimental… The quality of “Gold standard” in experimental studies can be achieved through Randomization Blinding Placebo
  45. 45. 45 Experimental… Randomization: random allocation of study subjects in to treatment & control groups Advantage: Avoids bias & confounding Increases confidence on results
  46. 46. 46 Experimental… Single blinding: Study subjects don’t know to which group they belong Double blinding: Physicians also don’t know to which group study subjects belong Triple blinding: Data collectors also don’t know allocation status Advantage: Avoids observation bias
  47. 47. 47 Experimental… Placebo: An inert material indistinguishable from active treatment Placebo effect: Tendency to report favourable response regardless of physiological efficacy Placebo is used as blinding procedure
  48. 48. 48 Screening Screening refers to the presumptive identification of a disease/defect by application of tests, examinations or other procedures in apparently healthy people.  Screening is an initial examination  Screening is not intended to be diagnostic
  49. 49. 49 Aims of screening program  Changing disease progression efficiently  Altering natural course of disease  Protecting society from contagious disease  Allocating resources rationally  Selection of healthy people for job  Studying the natural history of disease
  50. 50. 50 Criteria for establishing screening program  The problem should have public health importance  There should be accepted treatment for positives  Diagnostic & treatment facilities should be available  Recognized latent stage in the time course  Test is acceptable, reliable & valid  Natural history of the disease should be well understood  Case-finding is economical and continuous
  51. 51. 51 In general, a screening test should be Reliable & valid Sensitive & specific Simple & acceptable Effective & efficient
  52. 52. 52 Thank you!
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Fundamentals, Epidemiological methods and Study Design and conduct of Clinical Trials in Epidemiological set up.

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