Epidemiology
Learning Objectives for the Unit Having completed this unit, the student should    be able to: • Define epidemiology and l...
Learning Objectives for the Unit •   Describe study types used in epidemiology •   Identify the major sources of bias in  ...
Unit – 4 credit points•   Average student input per week:                                  5-6 hours•   Lectures (2 hours ...
Assessment• Sectional Test     Week 9      25%• Group  Assignment         Week 12     25%• Final Examination Week 15/16   ...
Text• Gordis, L. Epidemiology. WB Saunders  Co., Philadelphia, 2004 (3rd Edition)Other Readings
Contact detailsDr Aditi Dey Room T337, Level 3, T Block Phone 9351 9058, 9351 9494 Email A.Dey@fhs.usyd.edu.au
Lecture Outline• Introduction• Population Health & Disease Measures• Causation and Epidemiological Study  Types• Cohorts a...
Lecture Outline• Sources of Error:    – Selection & Measurement• Confounding•   Health Surveillance•   Disease Outbreaks• ...
Learning Objectives for today• Define epidemiology• List the uses of epidemiology• Describe key historical epidemiological...
Origin of the term ‘epidemiology’• epi - ‘on, upon, at, by, near, over, on top  of, against, among’• demos - ‘common peopl...
Definition of Epidemiology• ‘study of the distribution and determinants of health related states or events in specified po...
Epidemiology is aboutPopulations• Groups of people not individuals• It answers population questions  –   aetiology of dise...
Epidemiology and Clinical Practice    Practice of medicine is dependent on population    data. For example:•   A physician...
Example: PrognosisA patient may ask a doctor, “How long will I  live?’’The doctor usually answers on the basis of :• Exper...
Relationship between Epidemiology       and      Clinical MedicineStudies/Assessments           DiagnosisPrevention       ...
Examples of Epidemiological Studies(Use of observational data for prevention ofdisease)Vaccination: Prevention of smallpox...
Examples of EpidemiologicalStudies• Vaccination – Edward Jenner & the smallpox vaccination
First vaccination•Jenner took cowpoxmaterial from a dairymaid (Sarah Nelmes)and administered to an8-year old JamesPhipps•6...
• Jenner knew nothing about the biology of the disease or about viruses• He based his hypothesis from purely observational...
Examples of EpidemiologicalStudies• 1854 Outbreak of Cholera in London: sign at cemetery in Dudley, England
Epidemiology of cholera• John Snow and epidemiology of cholera• John Snow: anaesthesiologist who  administered chloroform ...
Cholera outbreak - map
• John Snow believed that cholera was caused by    contaminated water (others had other theories:    miasmatic theory)•   ...
Rates of cholera deathsWater Supply         Cholera Deaths per                       10,000 housesSouthwalk &             ...
The Broad Street pump              After the panic-              stricken officials              followed Snows           ...
Examples of Epidemiological Studies• Link between smoking and lung cancer                            Doll & Hill, 1964
Examples of Epidemiological StudiesWaterfluoridation:•Communitiesthat had lownatural waterfluoride levelshad high levelsof...
Trial in New York communities:Newburg and Kingston• DMF (decayed, missed and filled) index  was used.• Baseline informatio...
Rate of decayed teeth – regionaldifferences
• Water fluoridation is a controversial issue so after fluoride was added to its water supply, it was discontinued after a...
Decayed teeth – afterfluoridisation
Epidemiological Questions• When can we expect the next flu    epidemic?•   Are the number of AIDS cases increasing    or d...
Uses of Epidemiology(Gordis,2000)• Identifies aetiology or causes of disease  including the risk factors for the disease.•...
Uses of Epidemiology(Gordis,2000)• Describes and monitors the population health  and the patterns of disease• Evaluates ne...
Identifies aetiology or causes ofdisease including the risk factors for thedisease.                         Doll and Hill,...
Determine the extent of the diseasein the community                    NSW Health Survey,1997
Examines natural history of diseaseand prognosis of disease                   Figure 1: The Natural History of NIDDM      ...
Investigates and controls diseaseoutbreaks
Describes and monitors the populationhealth and the patterns of disease                      NSW Cancer Registry, 2002
Describes and monitors the populationhealth and the patterns of disease –breast cancer                              NSW Ca...
Evaluates new preventive andtherapeutic interventions and modes ofhealth care delivery •Has growth of managed care and oth...
Provides information to informpublic policy decisions - Smoking inrestaurants   Smokefree Environment Bill, 2000          ...
Determining Causation• Disease has been classically described as  a result of an epidemiological triad• It is the product ...
Determining Causation            Agent• Agent(s)  eg microorganisms,  chemicals,                     Disease  psychologica...
Determining Causation -Infection Agent: Beta-haemolytic                   streptococcus                   Disease    Host:...
Determining Causation - Chronic    Disease     - can be more complex    - usually the result of many factors (referred    ...
Causal Pathway or Causal Web                      Source: Stallones, R.A. (1966)
Risk Factor is:• An aspect of  –   personal behaviour or  –   Lifestyle or  –   environmental exposure or  –   an inborn o...
Risk Factor (major categories)BEINGS model by Jekel et al 2001•   Biological & behavioural factors•   Environmental factor...
Defining Populations inEpidemiology• Epidemiology focuses on defined  population and measures disease  outcomes & health i...
Example• In a survey of hang-gliding accidents it was    recommended that flying should be banned    between 11am and 3pm ...
Example• Accidents during 11am and 3pm  –   50 accidents per 200 people gliding  –   1 in 4 people = 25%• Accidents outsid...
Types of Populations• Population at Risk = People, healthy or sick who have the potential to develop a particular health s...
Cohort Populations• Also called fixed populations• Criteria for membership: experienced an    event or set of events•   On...
Dynamic Population• Have to meet certain criteria to be part  of the population• Membership only lasts while the  qualifyi...
Dynamic Population• Can be in a steady state when a specific    feature remains constant despite changing    membership.• ...
Key components ofepidemiological studies    Target  Population   Exposure to a study                     factor    Study  ...
Key components ofepidemiological studies• Target population is the population a  researcher wants to make  generalizations...
Key components ofepidemiological studies    Target  Population   Exposure to a study                     factor    Study  ...
Key components ofepidemiological studies• Study factor  – is a element that is being investigated to see if it is    a det...
• Exposure is contact with or possessing a particular study factor• Exposed group is a group whose members have had contac...
Key components ofepidemiological studies• Unexposed group is a group that has  not had contact with a cause of, or  posses...
Conclusions Based onComparisons• Clues to aetiology come from comparing  disease rates in groups with differing  levels of...
Proportion of Deaths Attributable to Tobacco,    NSW, 1996-1998 (Close & Achat)Cause of Death       Western           NSW ...
Next week• Population Health and Disease Measures  –   incidence  –   prevalence  –   death rates  –   standardisationText...
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Epi of IHD

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  • the first significant step in the fight against infectious disease was made in 1796 with discovery of a vaccine to prevent smallpox by Edward Jenner. Jenner had become aware of the fact that milkmaids who had suffered from a mild illness, cowpox, were unlikely to catch the much more serious smallpox disease.
  • To test his theory, Jenner infected his gardener's son, James Phipps, with cowpox and then weeks later attempted to infect him with the deadly smallpox. Happily, James survived the experience and was protected from infection and thus the practice of vaccination was born. Vaccines are medications that are designed to stimulate the body's immune system to generate a response that will protect the individual from disease by the pathogen in question.
  • In 1800s infections such as cholera were thought to spread via the inhalation of contaminated vapours. A surgeon named John Snow thought otherwise – he suspected it was spread by infected water In 1854, when Cholera struck England once again, Snow was able to legitimate his argument that Cholera was spread through contaminated food or water.
  • Snow, in investigating the epidemic, began plotting the location of deaths related to Cholera (see illustration). At the time, London was supplied its water by two water companies. One of these companies pulled its water out of the Thames River upstream of the main city while the second pulled its water from the river downstream from the city. A higher concentration of Cholera was found in the region of town supplied by the water company that drew its water form the downstream location. Water from this source could have been contaminated by the city's sewage. Furthermore, he found that in one particular location near the intersection of Cambridge and Broad Street, up to 500 deaths from Cholera occurred within 10 days.
  • Snow, in investigating the epidemic, began plotting the location of deaths related to Cholera (see illustration). At the time, London was supplied its water by two water companies. One of these companies pulled its water out of the Thames River upstream of the main city while the second pulled its water from the river downstream from the city. A higher concentration of Cholera was found in the region of town supplied by the water company that drew its water form the downstream location. Water from this source could have been contaminated by the city's sewage. Furthermore, he found that in one particular location near the intersection of Cambridge and Broad Street, up to 500 deaths from Cholera occurred within 10 days.
  • After the panic-stricken officials followed Snow's advice to remove the handle of the Broad Street Pump that supplied the water to this neighborhood, the epidemic was contained. Through mapping the locations of deaths related to Cholera, Snow was able to pinpoint one of the major sources of causation of the disease and support his argument relating to the spread of Cholera. Snow's classic study offers one of the most convincing arguments of the value of understanding and resolving a social problem through the use of spatial analysis. Nonetheless, there is some controversy regarding whether Snow made the map prior to or after the removal of the pump handle and about the timing of this removal relative to the temporal pattern of cholera deaths. While mapping has become a standard research approach in medical geography and epidemiology, today's researchers express the incidence of disease as a rate relative to the population or to the population within age cohorts (e.g., deaths per 1,000 population) so as to factor out the influence of population density. Using such refinements to the methods employed by Snow, mapping and spatial statistical techniques assist medical practitioners in understanding the diffusion and spread of diseases within communities and across the globe.  
  • the first significant step in the fight against infectious disease was made in 1796 with discovery of a vaccine to prevent smallpox by Edward Jenner. Jenner had become aware of the fact that milkmaids who had suffered from a mild illness, cowpox, were unlikely to catch the much more serious smallpox disease. To test his theory, Jenner infected his gardener's son, James Phipps, with cowpox and then weeks later attempted to infect him with the deadly smallpox. Happily, James survived the experience and was protected from infection and thus the practice of vaccination was born. Vaccines are medications that are designed to stimulate the body's immune system to generate a response that will protect the individual from disease by the pathogen in question.
  • the first significant step in the fight against infectious disease was made in 1796 with discovery of a vaccine to prevent smallpox by Edward Jenner. Jenner had become aware of the fact that milkmaids who had suffered from a mild illness, cowpox, were unlikely to catch the much more serious smallpox disease. To test his theory, Jenner infected his gardener's son, James Phipps, with cowpox and then weeks later attempted to infect him with the deadly smallpox. Happily, James survived the experience and was protected from infection and thus the practice of vaccination was born. Vaccines are medications that are designed to stimulate the body's immune system to generate a response that will protect the individual from disease by the pathogen in question.
  • the first significant step in the fight against infectious disease was made in 1796 with discovery of a vaccine to prevent smallpox by Edward Jenner. Jenner had become aware of the fact that milkmaids who had suffered from a mild illness, cowpox, were unlikely to catch the much more serious smallpox disease. To test his theory, Jenner infected his gardener's son, James Phipps, with cowpox and then weeks later attempted to infect him with the deadly smallpox. Happily, James survived the experience and was protected from infection and thus the practice of vaccination was born. Vaccines are medications that are designed to stimulate the body's immune system to generate a response that will protect the individual from disease by the pathogen in question.
  • the first significant step in the fight against infectious disease was made in 1796 with discovery of a vaccine to prevent smallpox by Edward Jenner. Jenner had become aware of the fact that milkmaids who had suffered from a mild illness, cowpox, were unlikely to catch the much more serious smallpox disease. To test his theory, Jenner infected his gardener's son, James Phipps, with cowpox and then weeks later attempted to infect him with the deadly smallpox. Happily, James survived the experience and was protected from infection and thus the practice of vaccination was born. Vaccines are medications that are designed to stimulate the body's immune system to generate a response that will protect the individual from disease by the pathogen in question.
  • refer to the actions of risk factors acting individually, in sequence, or together that result in disease in an individual. These pathways are often different with different sets of risk factors for individuals in different situations.
  • Epi of IHD

    1. 1. Epidemiology
    2. 2. Learning Objectives for the Unit Having completed this unit, the student should be able to: • Define epidemiology and list its uses • Describe the key features of epidemiology • Describe the basic measures used in epidemiology • Calculate measures of disease frequency • Interpret epidemiological data • Define and calculate measures of association
    3. 3. Learning Objectives for the Unit • Describe study types used in epidemiology • Identify the major sources of bias in research studies • Define the keys elements of a health surveillance system • Describe the key aspects of an outbreak investigation • Assess information on the effectiveness of screening programs • Assess the overall quality of a published report of an epidemiological study
    4. 4. Unit – 4 credit points• Average student input per week: 5-6 hours• Lectures (2 hours each week)• Tutorials (1 hour each week).• It is expected that students will attend classes.
    5. 5. Assessment• Sectional Test Week 9 25%• Group Assignment Week 12 25%• Final Examination Week 15/16 50% (2 hours) All assessments must be completed and submitted to pass the unit.
    6. 6. Text• Gordis, L. Epidemiology. WB Saunders Co., Philadelphia, 2004 (3rd Edition)Other Readings
    7. 7. Contact detailsDr Aditi Dey Room T337, Level 3, T Block Phone 9351 9058, 9351 9494 Email A.Dey@fhs.usyd.edu.au
    8. 8. Lecture Outline• Introduction• Population Health & Disease Measures• Causation and Epidemiological Study Types• Cohorts and Case- Control Studies and measures of association• Randomised Controlled Trials• Ecological studies and Cross Sectional Surveys
    9. 9. Lecture Outline• Sources of Error: – Selection & Measurement• Confounding• Health Surveillance• Disease Outbreaks• Critical Appraisal• Screening• Using Epidemiology to Evaluate Health Services/Review
    10. 10. Learning Objectives for today• Define epidemiology• List the uses of epidemiology• Describe key historical epidemiological studies• Explain the key features of epidemiological studies
    11. 11. Origin of the term ‘epidemiology’• epi - ‘on, upon, at, by, near, over, on top of, against, among’• demos - ‘common people or citizenry’• ology - ‘the study of’• epidemiology =‘Study of disease among the population’
    12. 12. Definition of Epidemiology• ‘study of the distribution and determinants of health related states or events in specified populations and the application of this study to the control of health problems’ Last, 1995
    13. 13. Epidemiology is aboutPopulations• Groups of people not individuals• It answers population questions – aetiology of disease – prevention of disease – Extent/distribution of disease (allocation of effort & resources in health facilities and communities)
    14. 14. Epidemiology and Clinical Practice Practice of medicine is dependent on population data. For example:• A physician hears a apical systolic murmur and knows it represents mitral regurgitation.• How does this knowledge originate?• The diagnosis is based on association of auscultatory findings with the findings of surgical pathology or autopsy in a large group of patients. Hence, diagnosis is population based
    15. 15. Example: PrognosisA patient may ask a doctor, “How long will I live?’’The doctor usually answers on the basis of :• Experience with large groups of patients who had the same disease• Were observed at the same stage of disease and received the same treatment
    16. 16. Relationship between Epidemiology and Clinical MedicineStudies/Assessments DiagnosisPrevention TreatmentEvaluation CurePlanning Care
    17. 17. Examples of Epidemiological Studies(Use of observational data for prevention ofdisease)Vaccination: Prevention of smallpox• Edward Jenner observed that dairy maids (women who milked cows) developed a mild disease called cowpox.• Later, in outbreaks of smallpox, these dairy maids did not develop smallpox and overheard one of them say, “I can’t take smallpox for I already had the cowpox.’’ This information was observational.• Jenner decided to test the hypothesis that cowpox could provide protection against smallpox.
    18. 18. Examples of EpidemiologicalStudies• Vaccination – Edward Jenner & the smallpox vaccination
    19. 19. First vaccination•Jenner took cowpoxmaterial from a dairymaid (Sarah Nelmes)and administered to an8-year old JamesPhipps•6 weeks later, Jennerinoculated the childwith material nowtaken from a smallpoxpustule.•The child did notdevelop smallpox
    20. 20. • Jenner knew nothing about the biology of the disease or about viruses• He based his hypothesis from purely observational data
    21. 21. Examples of EpidemiologicalStudies• 1854 Outbreak of Cholera in London: sign at cemetery in Dudley, England
    22. 22. Epidemiology of cholera• John Snow and epidemiology of cholera• John Snow: anaesthesiologist who administered chloroform to Queen Victoria in childbirth• In the 1st week of September, 1854 about 600 people died from cholera.• These people lived within a few blocks of the Broad Street pump in London
    23. 23. Cholera outbreak - map
    24. 24. • John Snow believed that cholera was caused by contaminated water (others had other theories: miasmatic theory)• In London at that time, a person obtained water by signing up with one of the water supply companies.• The intake for the water companies was a very polluted part of Thames river.• One of the companies (Lambert Company) shifted its water intake upstream in the Thames to a less polluted part of the river but the others didn’t.• Snow hypothesised that: mortality from cholera would be lower in people getting water from Lambert Company than those getting water from other companies
    25. 25. Rates of cholera deathsWater Supply Cholera Deaths per 10,000 housesSouthwalk & 315VauxhallLambeth Co 38Other districts in 56London
    26. 26. The Broad Street pump After the panic- stricken officials followed Snows advice to remove the handle of the Broad Street Pump that supplied the water to this neighbourhood, the epidemic was contained.
    27. 27. Examples of Epidemiological Studies• Link between smoking and lung cancer Doll & Hill, 1964
    28. 28. Examples of Epidemiological StudiesWaterfluoridation:•Communitiesthat had lownatural waterfluoride levelshad high levelsof dental caries•Communitiesthat had highnatural waterfluoride levelshad low levelsof dental caries
    29. 29. Trial in New York communities:Newburg and Kingston• DMF (decayed, missed and filled) index was used.• Baseline information from both communities collected• Water in Newburg was fluoridated and children re-examined• DMF index in Newburg had dropped after 10 years
    30. 30. Rate of decayed teeth – regionaldifferences
    31. 31. • Water fluoridation is a controversial issue so after fluoride was added to its water supply, it was discontinued after a referendum in Wisconsin (USA)• The next figure shows that after fluoride was removed, the DMF index rose• This provided further evidence that fluoride acted to prevent dental caries
    32. 32. Decayed teeth – afterfluoridisation
    33. 33. Epidemiological Questions• When can we expect the next flu epidemic?• Are the number of AIDS cases increasing or decreasing?• Should we screen the male population for prostate cancer?• How can cervical cancer best be prevented?• Has the slip, slap, slop campaign reduced skin cancers rates?
    34. 34. Uses of Epidemiology(Gordis,2000)• Identifies aetiology or causes of disease including the risk factors for the disease.• Determine the extent of the disease in the community• Examines natural history of disease and prognosis of disease
    35. 35. Uses of Epidemiology(Gordis,2000)• Describes and monitors the population health and the patterns of disease• Evaluates new preventive and therapeutic interventions and modes of health care delivery• Provides information to inform public policy decisions
    36. 36. Identifies aetiology or causes ofdisease including the risk factors for thedisease. Doll and Hill,1964
    37. 37. Determine the extent of the diseasein the community NSW Health Survey,1997
    38. 38. Examines natural history of diseaseand prognosis of disease Figure 1: The Natural History of NIDDM Modifiable: Modifiable: Modifiable: Poor glucose control Risk Inactivity Undiagnosed onset of complications Inactivity Factors Obesity Untreated progression of complications Obesity Non-Modifiable: Poor glucose control Fat Intake Genetics Hypertension Hypertension Age Dyslipidaemia Dyslipidaemia Poor Footcare Poor Footcare Smoking Smoking Non-Modifiable: Non-Modifiable: Genetics Genetics Disease Duration Healthy Development of Onset of complicationsNatural History Population End-Stageof NIDDM Onset of NIDDM Complications (Often asymptomatic) (Blindness, ESRF, Heart Attack, Amputations) Population at Risk Ongoing Primary Manage NIDDM Treat Complications Rehabilitation and Screening for Prevention Glucose Control Glucose Control Palliation complications Increase Activity Education Education Dialysis Eyes Improve Nutrition Increase Activity Increase Activity Post Amputation Feet Weight Control Reduce Obesity Reduce Obesity Rehab CVDPossible Diet Modification Kidneys Treat Hypertension Cardiac Rehab Treat Hypertension Treat Hyperlipidaemia Stroke RehabIntervention Points Treat Hyperlipidaemia Treat Retinopathy Aids Screen for NIDDM Self care Treat Vascular Problems Support in at risk populations Reduce Smoking Self care Reduce Smoking
    39. 39. Investigates and controls diseaseoutbreaks
    40. 40. Describes and monitors the populationhealth and the patterns of disease NSW Cancer Registry, 2002
    41. 41. Describes and monitors the populationhealth and the patterns of disease –breast cancer NSW Cancer Registry, 2002
    42. 42. Evaluates new preventive andtherapeutic interventions and modes ofhealth care delivery •Has growth of managed care and other new approaches to health care delivery had an impact on the patients’ QOL? •Does screening women with MRI for breast cancer improve survival for women?
    43. 43. Provides information to informpublic policy decisions - Smoking inrestaurants Smokefree Environment Bill, 2000 NSW Health Survey,1997
    44. 44. Determining Causation• Disease has been classically described as a result of an epidemiological triad• It is the product of an interaction of the human host, an agent (eg infectious) and the environment that promotes the exposure• For such an interaction to occur, the host must be susceptible
    45. 45. Determining Causation Agent• Agent(s) eg microorganisms, chemicals, Disease psychological factors Host Environment• Environment Factors physical, social or biological environment circumstances• Host Factors – susceptibility eg immunity, behaviours• Vectors of diseases: insects such as mosquitoes, arthropods (ticks) etc
    46. 46. Determining Causation -Infection Agent: Beta-haemolytic streptococcus Disease Host: Environment Low immunity Poverty, climateDisease: Acute rheumatic fever(polyarthritis, subcutaneous nodules over
    47. 47. Determining Causation - Chronic Disease  - can be more complex - usually the result of many factors (referred to as risk factors) acting in sequence, or     together that result in disease in an individual.
    48. 48. Causal Pathway or Causal Web Source: Stallones, R.A. (1966)
    49. 49. Risk Factor is:• An aspect of – personal behaviour or – Lifestyle or – environmental exposure or – an inborn or inherited characteristic that is associated with an increased occurrence of disease or other health-related event or condition.
    50. 50. Risk Factor (major categories)BEINGS model by Jekel et al 2001• Biological & behavioural factors• Environmental factors• Immunological factors• Nutritional factors• Genetic factors• Services, Social & Spiritual factors
    51. 51. Defining Populations inEpidemiology• Epidemiology focuses on defined population and measures disease outcomes & health in relation to a population at risk• Population at Risk = People, healthy or sick have potential to develop a particular health state or illness.• They would be counted as cases if they had the disease being studied
    52. 52. Example• In a survey of hang-gliding accidents it was recommended that flying should be banned between 11am and 3pm because this was when the greatest number (86%) of accidents occurred• During the month of May 1995: – 200 hang-gliders flew between the hours of 11am and 3pm – 50 accidents occurred during this time – 10 people flew outside the hours of 11am & 3pm – 8 accidents occurred during this time• Given this information, determine what time you are most likely to have an accident?
    53. 53. Example• Accidents during 11am and 3pm – 50 accidents per 200 people gliding – 1 in 4 people = 25%• Accidents outside the hours of 11am & 3pm – 8 accidents 10 people flew occurred during this time – 4 in 5 people = 80%
    54. 54. Types of Populations• Population at Risk = People, healthy or sick who have the potential to develop a particular health state or illness.• Populations may also be defined as: – cohort or – dynamic populations
    55. 55. Cohort Populations• Also called fixed populations• Criteria for membership: experienced an event or set of events• Once the qualifying events have been experienced by the person, membership of the cohort becomes a permanent• Examples: – a birth cohort may consist of all people born in 1973; – people who have a tertiary degree.
    56. 56. Dynamic Population• Have to meet certain criteria to be part of the population• Membership only lasts while the qualifying criteria are present, membership may be only temporary• Examples: – people attending university – membership is temporary
    57. 57. Dynamic Population• Can be in a steady state when a specific feature remains constant despite changing membership.• Example: – if 51% of a dynamic population is female and this remains constant over time (eg some women die and some women are born) - the population has a steady state in respect to gender composition• Are people in clinical trials a cohort or dynamic population?
    58. 58. Key components ofepidemiological studies Target Population Exposure to a study factor Study Exposed Population/ Outcome Sample Unexposed
    59. 59. Key components ofepidemiological studies• Target population is the population a researcher wants to make generalizations about• Study population is the group a researcher wishes to study (sometimes the same as the target population)• Study sample is a group of subjects chosen for study to represent the study population
    60. 60. Key components ofepidemiological studies Target Population Exposure to a study factor Study Exposed Population/ Outcome Sample Unexposed
    61. 61. Key components ofepidemiological studies• Study factor – is a element that is being investigated to see if it is a determinant of a particular health problem – or if it reduces the impact of a particular health problem. – Study factors can include • risk factors for a health problem, • interventions (therapeutic or preventative) to ameliorate a health condition, • diagnostic tests or techniques and • environmental exposures.
    62. 62. • Exposure is contact with or possessing a particular study factor• Exposed group is a group whose members have had contact with or possess a study factor
    63. 63. Key components ofepidemiological studies• Unexposed group is a group that has not had contact with a cause of, or possess a characteristic that is a determinant of, a particular health problem.• Outcome is any or all of the possible results that may stem from an exposure or study factor.
    64. 64. Conclusions Based onComparisons• Clues to aetiology come from comparing disease rates in groups with differing levels of exposure• Clues will be missed or false clues created if comparisons are biased by unequal collection of cases or exposure levels
    65. 65. Proportion of Deaths Attributable to Tobacco, NSW, 1996-1998 (Close & Achat)Cause of Death Western NSW SydneyLung Cancer 31.3 29.3Other cancer 8.5 9.0Coronary heart 22.9 20.6diseaseRespiratory 24.9 27.7disease
    66. 66. Next week• Population Health and Disease Measures – incidence – prevalence – death rates – standardisationText: P31-59
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