Principles of Epidemiology

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Principles of Epidemiology
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Principles of Epidemiology Course Note Cards
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  1. Define Epidemiology
    The study of the distribution and determinants of a disease frequency and health-related states in populations, and the application of this study to control health problems.
  2. Define Health
    Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.
  3. What is public health?
    Science and art of promoting health and extending life at the population level.

    Concerned with threats to health in the population or a group of people sharing one or more characteristics.

    Ensure conditions that promote the six dimensions of health in the population as a whole.
  4. What are the six dimensions of health?
    • 1)Physical
    • 2)Social
    • 3)Mental
    • 4)Emotional
    • 5)Spiritual
    • 6)Environmental
  5. What is the difference between medicine vs. Epidemiology?
    Medicine - clinician concern for the health of an individual

    Epidemiologist - concern for the collective health of the people in a community or population under study.
  6. What are the 5 main objectives of epidemiology?
    1) To identify the cause of disease and its risk factors

    2) To determine the extent of disease found in the community

    3) To study the natural history and prognosis of disease

    4) To evaluate new preventative and therapeutic measures

    5) To provide a foundation for developing public policy
  7. What is manifestation criteria?
    Symptoms, signs, and other manifestations of the condition. Relies on the proposition that diseases have a characteristic set of manifestations.

    Defines disease in terms of labeling symptoms.

    Only identifies patients in advanced stages

    Lost time because patient doesn't always show symptoms right away.
  8. What is causal criteria?
    Etiology of the condition, which, must have been identified in order to be employed. 

    Defines disease in terms of underlying pathological etiology.

    Mental health issues can be difficult because we don't always have a test to confirm them.
  9. What is the natural history of disease? (Stages)
  10. What is a notifiable disease in the US?
    • Cause of serious morbidity or death
    • Have the potential to spread
    • Can be controlled with appropriate intervention
  11. What is active Immunity?
    Body produces its own antibodies. This can occur through vaccines or in response to having a specific disease pathogen invade the body.
  12. What is passive immunity?
    Acquired through trans placental transfer of a mother's immunity to disease to the unborn child.
  13. What is herd immunity?
    If a population or group is mostly protected from disease by immunications (say 80% or more), then the chance of a major epidemic occurring is highly limited.
  14. Descriptive Epidemiology Questions
    • What
    • What are the health problems of the community?
    • What are the attributes of these illnesses?

    • Who
    • How many people are affected?
    • What are the attributes of the affected population?

    • When
    • Over what period of time?

    • Where
    • Where do the affected people live, work or spend leisure time?
  15. Types of Epidemiological Studies
  16. What are the three levels of prevention?
    • 1)Primary- occurs prior to exposure
    • immunizations
    • Sanitation
    • Education
    • Media Campaigns
    • Warning Labels
    • Infrastructure

    • Active Primary-Subject behavior change
    • Wearing protective devises
    • Health Promotion
    • Lifestyle Changes
    • Community Health Education

    • Passive Primary-Doesnt require behavior change
    • Vitamin fortified food
    • Fluoridation of public water

    • 2)Secondary-Reduce disease progress
    • Cancer Screening

    • 3)Tertiary-Reduce disability from disease
    • Physical Therapy
    • Halfway House
    • Shelter Homes
    • Fitness Programs
  17. Who was Hippocrates and what did he do?
    • Physician
    • Father of Medicine
    • First Epidemiologist
    • Physical activity changes risk factors
    • Seasonal change in disease
    • Introduced terms Epidemic and Endemic
  18. Who was Thomas Sydenham and what did he do?
    • Observation should drive the study of the course of disease
    • Useful treatments include:
    • exercise
    • fresh air
    • diet
    • Focused less on disease and more on cause
  19. Who was James Lind and what did he do?
    Applied experiemental method to identify that eating citrus fruits were effective remedies for scurvy among sailors.
  20. Who was Benjamin Jesty and what did he do?
    • Farmer/Dairyman
    • Noticed milkmaids never got smallpox but got cowpox
    • Exposed wife and children to cowpox (Variolation)
  21. Who was Edward Jenner and what did he do?
    Gave dairymaid mild case of cowpox in youth, by cutting her arm and rubbing some of the infectious "grease" into the wound. She did not get ill, but very unethical.
  22. Who was Ignaz Seemelweis and what did he do?
    • Basic Hygene
    • Importance of hand washing
  23. Who was Louis Pasteur and what did he do?
    • Cause of rabies
    • Studied Anthrax
    • Bacteria cause disease
    • Vaccine for anthrax
  24. Who was Robert Koch and what did he do?
    • Germ theory of disease
    • First picture of microbes
    • Microorganisms exist and cause disease
    • Anthrax was transmittable and reproducible
    • Spore stage growth cycle microorganisms
  25. Who was John Graunt and what did he do?
    • Systematically recorded age, sex, death records
    • Developed and calculated life tables & life expectancy
  26. Who was William Farr and what did he do?
    International classification of disease
  27. Who was Bernardino Ramazzini and what did he do?
    Identified work place hazards
  28. Who was Florence Nightingale and what did she do?
    treatment of soldiers, improved hygiene and treatment of them
  29. Who was Mary Mallon (Typhoid Mary) and what did she do?
    • Asymptomatic carry of typhoid fever
    • Importance of keeping track of carriers
  30. Who was T.K. Takaki and what did he do?
    • Eradicated beriberi
    • Kwashiorkor Disease- protein deficiency
  31. Who was Lemuel Shattuck and what did he do?
    • Sanitation infrastucture
    • Programs, Inspections, Sanitation Facilities
  32. Who was Jane Lane-Claypon and what did she do?
    • Breast Milk increase baby weight
    • Breast feeding decreased risk of cancer
    • Genes could influence cancer
  33. Who was Alice Hamilton and what did she do?
    • One of the first Occupational disease investigator
    • First woman appointed to Harvard medical school
  34. Who was Wade Hampton Frost and what did he do?
    • Analytical Science closely integrated with biology and medical science
    • Poliomyelitis
    • Influenza
    • Tuberculosis
    • Natural history of selected diseases
  35. Who was Doll and Hill and what did he do?
    unequivocal association between smoking and lung cancer (case-control)
  36. Who was Framingham Heart and what did he do?
    Diet and heart disease
  37. What are the three types of data surveillance?
    • Passive Surveillance - Sharing of health data between healthcare-related individuals.
    • Inexpensive
    • Likely to be incomplete
    • Timeliness concern
    • CDC Notifiable disease

    • Active Surveillance - Requires active involvement of public health agencies to collect health data.
    • Likely to be complete
    • Expensive
    • Time consuming
    • Undertaken during field investigation
    • CDC - Foodborne disease active surveillance network

    • Enhanced-Passive Surveillance - combination of passive and active.
    • Data being shared by all healthcare-related individuals, and organizations with public health agencies

    Public health agencies send notification to healthcare providers and facilities to remind them

    Often instituted during field investigation
  38. What are the type of public health Surveillance?
    Population Based-target population

    Community Based-community detect and report

    Hospital Based-condition requires level of care provided at hospital

    Laboratory Based-lab reports results for pathogens that cause disease

    School Based-Health related behavior or health conditions affecting children

    Sentinel Based-sample of reporting sites
  39. General Fertility Rate
    Used for comparisons of fertility among age, racial and socioeconomic

    Live births within a year/ # of women 15-44 *1000 women aged 15-44
  40. Crude Birth Rate
    Used to project population change, affected by the number and age composition of women of childbearing age

    • Live births/total population mid year *100 = CBR
  41. Infant Mortality Rate
    Used for international comparisons; a high rate indicates unmet health needs and poor environmental conditions

    # infant deaths among infant aged (0-365 days) during a year / # live births during year *100
  42. Cause Specific Rate
    Mortality/Frequency of disease/Population *100
  43. Population Mortality Rate (PMR)
    Indicates relative importance of specific cause of death; not a measure of the risk of dying of a particular cause.

    Mortality due to specific cause during time/Mortality due to cause during same time *100

  44. Attack Rate
    Used when there is an outbreak, usually infectious

    # cases of disease that develop/# pop risk start period
  45. Case Fatality Rate
    # Death/# Cases of Disease
  46. Survival Rate
    # Living/# Case of disease
  47. What are some of the problems with hospital data?
    • May not rep. entire population
    • Follow up with additional survey
    • Define population for denominator
  48. What is the measure of years of potential life lost (YPLL)?
    Measures the impact of mortality on society

    Sum (65 age at death)/People 65 younger*1000
  49. What are the disease frequency measures?
    • Numerator = Cases
    • Denominator = Pop at risk
    • Occurrence = Incidence and Prevalence
    • Incidence = Cummulative and Density
    • Prevalence = Point and Period
  50. What is prevalence?
    Quantifies number of existing cases of disease in a population at a point in time or during a period of time.

    • Point prevalence - specific point in time
    • Period prevalence - # people over period of time

    p=number existing cases/total pop
  51. What factors decrease prevalence?
    • Short duration
    • High case fatality
    • Decreased incidence
    • Out-migration of patients
    • Improved cure rate
  52. What is incidence?
    Quantifies number of new cases of disease that develop in a population at risk during a specified time period.

    # new cases/# people at risk
  53. What is cumulative incidence?
    • Estimates probability or risk that a person will develop a disease at specific time.
    • Assumes you have followed the entire population for the entire follow-up period.
    • # new cases/# candidate pop over specific time
  54. What is Incidence Rate (IR)?
    This measure is a true rate because it directly integrates time into the denominator. Also can be called incidence density.

    # new cases/person-time in candidate pop.
  55. Incidence and Prevalence comparison
  56. What is incidence?
    Measure of the risk of developing some new condition within a specified period of time.

    Measure of new cases of a disease that develop over a period of time.

    Incidence density(rate)
  57. What is prevalence?
    Proportion of a population found to have a condition (typically a disease or a risk factor such as smoking or seat-belt use).

    Measures existing cases of a disease at a particular point in time or over a period of time.

    Used to asses health status of a population

    Planning and health services

    Often only measure possible with chronic disease where cases cannot be easily detected

    Does not identify risk factors

    Makes no sense for acute or short duration diseases

    • Point Prevalence-one point in time
    • Period Prevalence-longer duration of time
  58. What do ratio, proportion, and rate mean?
    Ratio- division of one number by another

    Proportion- numerator is subset of denominator, often expressed as a percentage

    Rate- time is an intrinsic part of the denominator, term is most often misused.
  59. Prevalence Equation and Type of study design
    Cross-sectional study (e.g. Sample Surveys)

  60. Point Prevalence Equation
    P = C/N

    • C=# of observed cases at time t
    • N= Population size at time t
  61. What is Cumulative Incidence?
    • Most common way to estimate risk
    • Always a proportion (0 to 1)
    • Always assume fixed or closed cohort (no exit)
    • Attrition(lost to follow-up) is a huge issue
    • Formula does not represent dynamic changing population
    • Does not allow subjects to be followed over different time periods
  62. Cumulative Incidence Equation
    CI=I/N

    • I=# of new cases during follow-up
    • N=# of disease-free subjects at the start

    Measures the frequency of addition of new cases of disease and is always calculated for a given period of time (annual incidence)

    Always state the time period
  63. Incidence Density (Rate) Equation
    IR = I/PT

    • I=# of new cases during follow-up
    • PT=Total sum of the person-time of the at risk population

    Using person-time rather than just time handles situations where the amount of observation time differs between people, or when the population at risk varies with time.
  64. Risk Vs. Rate
    • Cumulative Incidence Vs. Incidence Density
    • Always between (0-1) Vs. non-negative and no upper bound
    • Probability individual will develop a disease during a specific period Vs.Describes how rapidly new events occur in a specific pop.
    • Individual prognosis Vs. ecological comparison
    • No variable follow-up times, attirtion, competing risks Vs. Variable follow-up, attrition, competing risks.
  65. What is the dependency ratio?
    Population <15 and 65+/Population 15-64*100

    Interpret -->There are ____dependents for every 100 people of working age.
  66. What is a crude rate?
    The crude mortality rate is the mortality rate from all causes of death for a population during a specified time period. The denominator is the population at the mid-point of the time period.
  67. What is mortality?
    a person who died or number of deaths
  68. What is morbidity?
    Latin morbidus, meaning "sick, unhealthy") is a diseased state, disability, or poor health due to any cause. The term may be used to refer to the existence of any form of disease, or to the degree that the health condition affects the patient.
  69. What are the two methods of rate adjustment?
    Direct - apply stratum specific rates observed in the populations of interest to a reference of standard population in order to obtain the number of deaths expected in the reference population. Calculate an adjusted rate based on expected number of deaths in the reference population

    Indirect - apply stratum specific reference rate to the populations of interest to obtain the number of expected deaths in each of those populations. Compare observed to expected
  70. What is direct age adjustment rate?
    • Example:
    • Age Adjusted rate per 1000 single males

    =Expected deaths in reference pop using single rates/ Total reference pop
  71. Specific or Stratified Rate
    Annual mortality rate from ____ per 1,000=

    • Total number of deaths from ___in one year/
    • number of persons in the population mid year *1,000
  72. Two by Two tables
  73. What is attributable risk?
    (risk exposed - risk unexposed)*100,000

    Interpret--> The excess occurrence of cardiovascular disease among male smokers attributable to their smoking is 43 per 100,000
  74. What is attributable risk %?
    is the percent of the incidence of a disease in the exposed that is due to the exposure. It is the proportion of the incidence of a disease in the exposed that would be eliminated if exposure were eliminated.

    ARP% = (relative risk - 1)/relative risk=%
  75. What is Population Attributable Risk %?
    Described as the reduction in incidence that would be observed if the population were entirely unexposed compared with its current (actual) exposure pattern

    PAR% = {(risk total- risk unexpo)/risk total * 100}
  76. Risk/Rate Difference (Attributable Risk)
  77. What are the 6 types of screening techniques?
    • Mass -Whole population groups
    • Selective - Selected high-risk groups
    • Multiple/Multi-phasic - two or more screening test are done in combination to large groups people
    • Surveillance - Continuous
    • Case-finding - Main object to detect disease and bring patients to treatment
    • Epi Surveys - Not for diagnostic purpose, but rather to find the prevalence in the population
  78. Types of prevention screenings
  79. What is screening?
    The testing of apparently well people to find those at increased risk of having a disease or disorder.

    • Disease appropriate for screening:
    • 1-sever consiquences
    • 2-treamtment more effective early on
    • 3-detectable preclinical phase
    • 4-preclinical phase is fairly long
    • 5-prevelance is well known
  80. What is reliability?
    Repeatability- get the same results each time from each instrument from each rater. Does not ensure validity.
  81. What is validity?
    Sensitivity - probability(proportion) of correct classification of cases. = Cases found/all cases or True positive / All cases or A/A+C   Screening by urine glucose test will identify ___% of all true diabetes cases.

    Specificity - probability(proportion) of correct classification of non-cases = non cases identified/ all non-cases or True Negatives/All non-cases or D/B+D     Screening by urine glucose test will correctly classify ____% of all non-diabetic cases as being disease free.

  82. What is PPV and NPV?
    • Positive Predictive Value (PPV)
    • Cases identified/all positive tests

    • Negative Predictive Value (NPV)
    • Non-cases identified/all negative tests

    A low cutoff point will have a few false negatives (high sensitivity) but many false positives (low specificity).

    High cutoff point will have many false negatives (low sensitivity) but few false positives (high specificity).
  83. What is Cohen's Kappa?
    Quantifies agreement above chance, two raters classify each item, then calculate k.

    K=2(ad-bc)/(p1*q2) + (p2*q1)

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