EPIDEMIOLOGY AND ITS CONTRIBUTION TO MEDICAL RESEARCH (selected slides)

Transcription

1 Department of Epidemiology, Medical University of Silesia EPIDEMIOLOGY AND ITS CONTRIBUTION TO MEDICAL RESEARCH (selected slides) Jan E. Zejda

2 TOPICS Roots of modern epidemiology Epidemiology among health sciences Definition of epidemiology Epidemiological paradigms Application of epidemiology in medical research Clinical epidemiology

3 TOPICS Roots of modern epidemiology Epidemiology among health sciences Definition of epidemiology Epidemiological paradigms Application of epidemiology in medical research Clinical epidemiology

4 CHOLERA IN EUROPE 1829 in Orenburg (Russia) 1830 in Moscow (Russia) 1831 Poland, Hungary, Austria, Prussia 1832 England, France, Scandinavia, Spain

5 CHOLERA IN EUROPE Second Wave of Epidemia 1848 in England: 53000

6 Dr WILLIAM FARR Physician Founder of Medical Statistics (measurement of health events: birth, mortality, etc.)

7 CHOLERA CARRIED BY AIR POLLUTED BY MIASMA (miasma = rotting organic matter) Farr s hypothesis ( miasma theory ) Deaths due to cholera versus elevation of the residence place in London Deaths Zgony/ < Stopy nad poziomem morza Feet above sea level Źródło: Gordis L.: Epidemiology. W.B. Sounders Company, Philadelphia 1996)

8 MIASMA THEORY (miasma in Greek = pollution) Thickness of miasma layer <20 Stopy nad poziomem morza Feet above sea level

9 DR JOHN SNOW One of the first physicians to test the use of ether and chloroform as anaesthetics. Designer of devices to safely administer ether and chloroform. C 2 H 5 OC 2 H 5 CHCl 3 Kidney Liver Heart

10 JOHN SNOW ( ) on causes of cholera epidemics in London

11 JOHN SNOW ( ) on causes of cholera epidemics in London Snow s statistical argument regarding water-borne disease Mortality distribution according to the place of residence / source of drinking water Water Supply Company Number of houses Number of deaths Deaths rate (n/10000 houses) Southwark&Vauxhall Lambeth Source: Fox J.P. et al.: Epidemiology. Man and Disease. The Macmillan Company, London 1970)

12 JOHN SNOW ( ) on causes of cholera epidemics in London

13 SNOW S DISTINCT METHODS Symptoms of acute intestinal infection (medical background) Location (plotting the cases) Measurement of mortality rates (comparisons) observation hypothesis measurement knowledge action

14 IMPORTANT MESSAGE Cholera put under control long before the causative agent was discovered response Establishment of General Health Department (London) International Health Conference (Paris) Public Health Act (Great Britain): water supply, sewage transportation, etc Establishment of International Health Organization (Paris)

15 ROBERT KOCH ( ) [Vibrio cholerae 1884]

16 Koch 1884!

17 FILIPPO PACINI ( ) [Vibrio Cholerae 1854]

18 EPIDEMIOLOGY TODAY (from infectious to non-infectious diseases) Ch. Niezakaźne Ch. Zakaźne Non-infectious diseases Infectious diseases YESTERDAY ADVANCES IN MEDICINE DEMOGRAPHY QUALITY OF LIFE TODAY

19 TOPICS Roots of modern epidemiology Epidemiology among health sciences Definition of epidemiology Epidemiological paradigms Application of epidemiology in medical research Clinical epidemiology

20 HEALTH SCIENCES RESEARCH FIELD PRIMARY FOCUS Health Services Epidemiology Clinical Sciences Biologic Sciences Health care systems Populations Individual patients Animal models, cells & transmitters, molecules, genes, drugs development Source: Fletcher R.W., Fletcher S.W.: Clinical Epidemiology. The essentials.lippincott Williams & Wilkins 2005

21 HEALTH SCIENCES RESEARCH FIELD PRIMARY FOCUS Health Services Epidemiology Clinical Sciences Biologic Sciences Health care systems Populations Individual patients Human & animal models, cells & transmitters, molecules, genes, drugs development Source: Fletcher R.W., Fletcher S.W.: Clinical Epidemiology. The essentials.lippincott Williams & Wilkins 2005

22 TOPICS Roots of modern epidemiology Epidemiology among health sciences Definition of epidemiology Epidemiological paradigms Application of epidemiology in medical research Clinical epidemiology

23 DEFINITION OF EPIDEMIOLOGY The study of the distribution and determinants of health related states or events in specified populations, and the application of this study to control of health problems (Last, 2001)!

24 EPIDEMIOLOGY The study of the distribution and determinants of health related states or events in specified populations, and the application of this study to control of health problems STUDY surveillance, observation, hypothesis testing, analytic research, and experiments.

25 EPIDEMIOLOGY The study of the distribution and determinants of health related states or events in specified populations, and the application of this study to control of health problems DISTRIBUTION analysis by person, place and time who where when?

26 EPIDEMIOLOGY The study of the distribution and determinants of health related states or events in specified populations, and the application of this study to control of health problems DETERMINANTS (function) risk factors, protective factors, modyfying factors

27 DETERMINANTS (source) HOST FACTORS SOCIO- ECONOMIC FACTORS ENVIRON- MENTAL FACTORS LIFE STYLE FACTORS OTHER FACTORS - Genes - Gender - Age - Poverty - Employment - Isolation - Air quality - Water quality - Occupational environment - Home environment - Social environment - Nutrition - Physical activity - Tobacco - Alcohol - Drugs - Sexual activity -Education -- Health care system - Transport. - Recreation

28 EPIDEMIOLOGY The study of the distribution and determinants of health related states or events in specified populations, and the application of this study to control of health problems HEALTH RELATED STATES OR EVENTS diseases, causes of death, behavior, reactions to preventive regimens, provision and use of health services

29 HEALTH-RELATED PHENOMENA

30 EPIDEMIOLOGY The study of the distribution and determinants of health related states or events in specified populations, and the application of this study to control of health problems APPLICATION TO CONTROL to assess the public health importance of diseases, identify the population at risk, identify the causes of disease, describe the natural history of disease, and evaluate the prevention and control of disease

31 EPIDEMIOLOGY The study of the distribution and determinants of health related states or events in specified populations, and the application of this study to control of health problems APPLICATION TO CONTROL health promotion preventive measures diagnostic standards therapeutic standards

32 EPIDEMIOLOGY versus CLINICAL MEDICINE PRINCIPAL TASKS CLINICAL MEDICINE EPIDEMIOLOGY Diagnosis Epidemiological study Treatment Prognosis Prevention, health promotion Risk assessment

33 EPIDEMIOLOGY FROM KNOWLEDGE Descriptive epidemiology (what, who, where..?) Analytical epidemiology (why?) TO APPLICATION Prevention New diagnostic / therapeutic procedures Refined provision of health services

34 TOPICS Roots of modern epidemiology Epidemiology among health sciences Definition of epidemiology Epidemiological paradigms Application of epidemiology in medical research Clinical epidemiology

35 EPIDEMIOLOGIC PARADIGMS Non-random occurrence of diseases Between-subject variability in health and exposures* leading to co-variability - a very broad concept (smoking=exposure; gene variant=exposure; etc..) & Reliability of the results

36 DISEASES DO NOT OCCUR BY RANDOM?? WHY ME? NON-RANDOM OCCURRENCE IMPLIES CAUSATION EXPOSURE TO WHAT? (HARMFUL AGENTS? POOR GENES??)??

37 Q: IS KNOWN HEALTH DISORDER RELATED TO KNOWN EXPOSURE? A: COVARIABILITY Y/N (1) Between-subject variability in health status (2) Between-subject variability in potential risk factors (1) follows (2) = covariability

38 Reliable Measurement of Health and Exposure Evidence of Covariability

39 SIR DAVID ROXBEE COX FOUR CHALLENGES: MEASUREMENT STUDY DESIGN DATA ANALYSIS INTERPRETATION David R. Cox: Some challenges for medical statistics (symposium Modern Statistical Methods in Medical Research - Nobel Foundation Series Frontiers in Medicine < European Journal of Epidemiology 2005;30:5-9 >

40 LORD KELVIN ( ) When you can measure what you are speaking about, and express it in numbers, you know something about it. But when you cannot your knowledge is of a meager and unsatisfactory kind (Lord Kelvin)

41 MEASUREMENT - Quantitative scale: blood glucose level - Qulitative scale: round opacity on chest x-ray SOURCES Interview, standardized questionnaire, laboratory tests, composed indices case definition

42 MEASUREMENT - ERRORS TYPE I: above, above, below, above, below, below, above, below, above, above TYPE II: either or above, above, above, above, above, above, above below, below, below, below, below, below, below Repeat measurements and you are close to the true value (average) Repeat measurements and you are always one way away from the true value RANDOM ERROR SYSTEMATIC ERROR (BIAS)

43 GOOD EPIDEMIOLOGY PRACTICE EPIDEMIOLOGICAL STUDY A MEASURING TOOL Prevalence of diabetes Role of sleep deprivation in high blood pressure Protective significance of face mask in COPD etc., etc. MEASUREMENT IS SUBJECT TO ERROR

44 RANDOM ERROR Divergence due to chance alone of an observation (measurement) on a sample from the true population value (estimate parameter). Three sources: Biological variation; Sampling error; Measurement error. Given biological variation and limited accuracy of the measurement random error can be reduced by increasing the size of the sample ( estimate obtained in a sample composed of all candidates = parameter)

45 SYSTEMATIC ERROR = BIAS Systematic divergence (either in plus or in minus ) of an observation (measurement) on a sample from the true population value (estimate parameter). Three principal classes of bias: Selection bias; Information bias; Confounding.

46 SELECTION BIAS Distortion resulting from the manner in which subjects are selected (from population to sample) Berkson s bias (hospital admission bias): affects studies done in hospitalized populations the relation found in hospital may not reflect the one in the population; Nonresponse bias: refusers are more likely to engage in unhealthy behaviors Healthy worker effect: seriously ill people are unable to join and remain in the workforce Way to avoid (minimize) = representative, probability sampling

47 INFORMATION BIAS Causes: measurement device defects, inappropriate questionnaires, inaccurate diagnostic procedures, Result: placement of a subject in a wrong category (misclassification) Recall bias: sick individuals are more likely to recall hazardous exposures, events, etc. (mothers of leukemia children remember all, mothers of healthy children do not care ) Diagnostic suspicion bias: increased diagnostic attention toward exposed (endometrial cancer versus hormone replacement therapy estrogens)

48 CONFOUNDING Distortion in an association between a study exposure and disease brought about by the influence of a third factor Confounder: Is associated with the exposure in question; Is an independent risk factor for the disease Confounder Exposure? Disease Is not intermediate in the causal pathway: exposure - disease

49 RANDOM ERROR AND SYSTEMATIC ERROR True Value of the Studied Event = bull s eye Result of the Study = dot Random Error (Imprecision) Low High Systemtic Error (Bias) Low High

50 VALIDITY Internal validity (state-of-art measurements on sample) External validity (generalizability) GOOD EPIDEMIOLOGY PRACTICE!

51 GOOD EPIDEMIOLOGY PRACTICE Identify potential sources of errors Avoid errors Control errors Adjust for errors

52 TOPICS Roots of modern epidemiology Epidemiology among health sciences Definition of epidemiology Epidemiological paradigms Application of epidemiology in medical research Clinical epidemiology

53 Core Contributions 1,2,3,4

54 EPI CONTRIBUTION TO MEDICAL RESEARCH I INVESTIGATION INTO NATURAL HISTORY OF DISEASES Good Health Subclinical Changes Clinical Disease Death or Recovery

55 EPI CONTRIBUTION TO MEDICAL RESEARCH II DESCRIPTION OF HEALTH STATUS OF POPULATION Occurrence of diseases (health events) Incidence Prevalence According to sex According to age According to According to sex According to age According to

56 EPI CONTRIBUTION TO MEDICAL RESEARCH III EXPLORATION OF CAUSATION Genetic factors Genetic factors Lifestyle factors Good Health Onset of disease Ill Health Lifestyle factors Environmental factors Environmental factors

57 EPI CONTRIBUTION TO MEDICAL RESEARCH IV EVALUATION OF INTERVENTION Treatment Good Health Ill Health Diagnostic Procedures Health promotion Preventive measures Public health services Medical Care

58 TOPICS Roots of modern epidemiology Epidemiology among health sciences Definition of epidemiology Epidemiological paradigms Application of epidemiology in medical research Clinical epidemiology

59 EPIDEMIOLOGY and CLINICAL MEDICINE CLINICAL MEDICINE EPIDEMIOLOGY Patient Population/Group Treatment HOWEVER Prevention, health promotion Prognosis Risk assessment Patient A responds to the treatment T, patient B does not, and patient C (what is the true effect of the treatment T?) Low level of enzyme E has a prognostic value in patient A and not in patient B (what is the true diagnostic value of enzyme E?)

60 EPIDEMIOLOGY and CLINICAL MEDICINE CLINICAL MEDICINE EPIDEMIOLOGY Treatment Prevention, health promotion CLINICAL EPIDEMIOLOGY Prognosis Risk assessment

61 CLINICAL EPIDEMIOLOGY The science of making predictions about individual patients by counting clinical events in groups of similar patients and using strong scientific methods to ensure that the predictions are accurate. The purpose of clinical epidemiology is to develop and apply methods of clinical observation that will lead to valid conclusions by avoiding being misled by systamatic error and the play of chance Source: Fletcher R.W., Fletcher S.W.: Clinical Epidemiology. The essentials.lippincott Williams & Wilkins 2005

62 CLINICAL EPIDEMIOLOGY Clinical because it seeks to answer questions and to guide clinical decisions making with the best available evidence Epidemiology because many of the methods used to answer the questions have been developed by epidemiologists (patient as a member of the population of patients disease specific) Source: Fletcher R.W., Fletcher S.W.: Clinical Epidemiology. The essentials.lippincott Williams & Wilkins 2005

63 CLINICAL EPIDEMIOLOGY ISSUES Abnormality Diagnosis Frequency Risk Prognosis Treatment Prevention Cause Source: Fletcher R.W., Fletcher S.W.: Clinical Epidemiology. The essentials.lippincott Williams & Wilkins 2005

64 FROM CO-EXISTENCE TO SYNERGISM EPIDEMIOLOGY vs CLINICAL MEDICINE EPIDEMIOLOGY CLINICAL MEDICINE