By Hatim Jaber MD MPH JBCM PhD 6+8 12- 2016

1. Faculty of MedicineIntroduction to Community Medicine Course(31505201)Unit 4 EpidemiologyIntroduction to EpidemiologyEPIDEMIOLOGICALSTUDY METHODS By HatimJaber MD MPH JBCM PhD 6+8 12- 2016

2. Presentation outline

3. Invisible and silent killers

4. Invisible killer AIR POLLUTION

5. Silent killer

6. Important “What you cant measure you cant control!” epidemiological study methods are used to study your health and my health and its determinants, as we join hands to ensure a healthier us.

7. INTRODUCTION • The science of epidemiology has matured significantly from the times of Hippocrates and john snow [physician] that the techniques for analyzing data vary depending on the type of disease being monitored but each study will have similarities. environmental factors can influence the occurrence of the diseases. • epidemiology study of what is upon the people • Derived from the greek terms epi=upon,among. demos=people, district. Logos study, word.

8. DEFINITION OF EPIDEMIOLOGY • Epidemiology is the study of distribution and determinant of health related state or event in a specified human population and the application of this study to the control of health problem.

9. EPIDEMIOLOGY [DEFINITION OF KEY TERMS] • Distribution : Frequency (including rates & risks) & pattern of health events(person, place, time) • Determinants : factors or events that are capable of bringing about a change in health • Human population : Epidemiology examines health events among population groups rather than individuals.

10. EPIDEMIOLOGY [DEFINITION OF KEY TERMS] • Health related states: infections, chronic diseases & physiological events &various states of health such as disability, injury, mortality • Health related events : immunization, hospital attendance, bed occupancy • Application : basis for directing interventions

11. CLASSIFICATION

12. CLASSIFICATION(CONT.) CORRELATIONAL

13. Epidemiologic Study Designs

14. Aims of Epidemiologic Research • Describe the health status of a population • To assess the public health importance of diseases • To describe the natural history of disease, • Explain the etiology of disease • Predict the disease occurrence • To evaluate the prevention and control of disease • Control the disease distribution Descriptive epidemiology Analytic epidemiology Applied epidemiology

15. Descriptive and Analytical Epidemiology • Descriptive epidemiology • Describes the occurrence of disease (cross-sectional) • Analytic epidemiology: • Observational (cohort, case control, cross-sectional, ecologic study) – researcher observes association between exposure and disease, estimates and tests it • Experimental(RCT, quasi experiment) – researcher assigns intervention (treatment), and estimates and tests its effect on health outcome

16. OBSERVATIONAL VS EXPERIMENTAL STUDIES • Observational studies Allow nature to take its cause; the investigator measures but does not intervene • Descriptive study: focuses on the description of the occurrence of a disease in a population • Analytical study analyses relationships between health status and other variables

17. OBSERVATIONAL VS EXPERIMENTAL STUDIES • Experimental or interventional studies: involve an active attempt to change a disease determinant(e.g an exposure or a behaviour) or the progress of a disaese (through treatment) • The studies are based on a group which has had the experience compared with control group which has not had the experience.

18. PURPOSE OF DESCRIPTIVE EPIDEMIOLOGY • To generate hypothesis • To permit evaluation of trends in health & disease and comparisons among countries and subgroups within countries. • To provide a basis for planning, provision and evaluation of health services • To identify problems to be studied by analytical methods and to suggest areas that may be fruitful for investigation

19. CASE STUDIES(CASE SERIES) • Case reports:documents unusual medical occurrence and can represent the first clues to the formulation of hypothesis, generally report a new or unique findings and previous undescribed disease. • Case series: collection of individual case reports which may occur within a fairly short time,and experience of a group of patients with similar diagnosis.

20. Case Series • Advantages • Useful for hypothesis generation • Informative for very rare disease with few established risk factors • Usually of short duration. • Disadvantages • Cannot study cause and effect relationships • Cannot assess disease frequency

21. CROSS-SECTIONAL STUDY • It is also called epidemiologic study or prevalence study • It analyses (describes)data collected on a group of subjects at one point in time rather than over a period of time. i.e they survey exposure and disease at a single point in time. • Both exposure and outcome variables are been evaluated at the same point in time(without any inbuilt directionality) • Most sophisticated descriptive study • It answers the question “WHAT IS HAPPENING RIGHT NOW?”

22. o onset time end Question: “what is happening?”no direction of inquiry

23. CROSS-SECTIONAL STUDY ADV • Best for determining the status quo(prevalence) • Quick • Relatively inexpensive DISADV • Only a snapshot at a time leading to a misinformation • Response rate may be low ,with result not representative of the population

24. Cross-sectional studies • Disadvantages • Weakest observational design, (it measures prevalence, not incidence of disease). Prevalent cases are survivors • The temporal sequence of exposure and effect may be difficult or impossible to determine • Usually don’t know when disease occurred • Rare events a problem. Quickly emerging diseases a problem

25. CORRELATIONAL STUDY DESIGN • A study comparingincidence/prevalence of one event against another on a global scale • Measures that represent characteristics of entire populations are used to describe the disease in relation to some factor of interest (such as age, calendar time, food consumption, drug use and utilization of health services)

26. CORRELATIONAL STUDY DESIGN DISADV Doesn’t compare individuals, so it might lead to overgeneralization. ADV • Compares events among nations

27. Number of Ill persons (new cases) Population at risk exposed Attack rate = Which Disease if More Important to Public Health? Measure of Disease Occurence • Attack rate is a Cumulative Incidence; it shows the risk (probability) of disease to occur in a population • In regard to risk, measles is the most important disease to public health while rubella being the least

28. Description of Disease Distribution in the Population Disease reaches its peak in frequency in Week 6 Disease affects mostly people under five years of age Disease affects people living alongside the river

29. ANALYTICAL STUDIES Two basic designs: • Case – control or retrospective study • Cohort or prospective NOTE • There must be a comparison group • No control No conclusion(NCNC)

30. CASE CONTROL OR CASE HISTORY STUDY • A group of affected people is compared to unaffected people(the control) • It’s a LONGITUDNAL STUDY (like cohort study) because it’s a study over a period of time. • Subjects are selected based on a particular outcome and a study backwards in time to try to detect the causes or risk factors that may have earlier been reported in a descriptive study • Subjects are then matched and assigned into the two groups. Subject selected on the basis of disease[e.g lung cancer]. • Sometimes called a retrospective study because of the direction of study

31. CASE CONTROL OR CASE HISTORY STUDY

32. Advantages of case control • It is relatively easy to carry out bcos we go back to existing records in the hospital • It is also rapid and inexpensive • It requires comparatively few subjects • It can assist one in studying different etiological factors • One does not need an ethical clearance • There is no risk to the subject

33. Disadvantages of case control • It introduces bias • To select an appropriate control could be difficult • It may be difficult to distinguish between the cause of a disease and an associated factor

34. COHORT STUDY • A cohort is a group of people who have something in common and remain part of a group over an extended time • A group of people exposed to a suspected etiological agent are compared with a matched control who have not been similarly exposed. Subject selected on the basis of exposure [etiological factor; cigarette smoking] • Follow-up over a period to compare the outcome • Also a longitudinal study or prospective study

35. Cohort Design disease Factor present no disease Study population free of disease disease Factor absent no disease present future time Study begins here

37. ADVANTAGES OF COHORT • There is no bias • The risk can be calculated -the incidence can be calculated • It is effective for studying rare exposures • It allows the study of the natural history of the disease • It assists in determining the temporal relationship between the etiological factor & the disease

38. Disadv of cohort study • It takes a long time • It is expensive • Large number of subjects are needed • There could be changes in the standard methods or diagnostic criteria

39. EXPERIMENTAL STUDIES • Studies in which 1 group is deliberately subjected to an experience compared with a control group with no similar experience • The gold standard in medicine -it proves causality • Can be controlled or uncontrolled

40. UNCONTROLLED EXPERIMENTAL STUDIES • Intervention is not compared with a control • The aim is to confirm that the Intervention made a difference

41. CONTROLLED EXPERIMENTAL STUDIES • In this study, a drug or procedure is compared to: • Another drug • Procedure • Placebo • Previously accepted tx • The aim is to proove the difference due to tx

42. CONTROLLED EXPERIMENTAL STUDIES • Blind trial-single or double • Control could be: • METHODOLOGY • Concurrent or parallel: randomized or non- randomized(quasi) • Sequential control: self controlled or cross over • External control

43. B. STUDY POPULATION • Clinical trials • Field trials • Community trials

44. EXPERIMENTAL STUDIES ADV DISADV Greatest expense Long duration Unproven facts adopted by community can hinder study acceptance • Best study type • Greatest prove of causality • Gold standard for other design • Least bias • Proves best treatment or procedure efficacy

45. overview

46. Study Design and Its Strength of Evidence • Systematic review, meta-analysis: secondary data analysis • Randomized Controlled Trials (RCT) • Cohort: prospective or retrospective Quasi experiment • Case control: prospective or retrospective • Cross sectional • Case Reports / Case Series Strongest evidence Weakest evidence

49. Epidemiologic Measures of Association • Compute & Interpret Relative risk (RR) & Odds ratio (OR) as a measure of association between exposure and Disease • Understand when OR approximates RR

50. Definitions Association • A statistical relationship between two or more variables Risk • Probability conditional or unconditional of the occurrence of some event in time • Probability of an individual developing a disease or change in health status over a fixed time interval, conditional on the individual not dying during the same time period Absolute risk