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Introduction to Epidemiology > Part I: Fundamentals of Epidemiology > Flashcards

Part I: Fundamentals of Epidemiology Flashcards

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1
Q

Epidemiology

A

The study of the distribution and determinants of disease frequency in human populations and application to control health problems

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2
Q

Population

A

Group of individuals with a shared characteristic

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3
Q

Distribution

A

Analysis of disease patterns according to person, place, and time

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4
Q

Objectives of Epidemiology

A
  1. Identify Causes of Disease and risk factors
  2. Determine extent of disease in community
  3. Examine natural history of disease
  4. Evaluate effectivness of interventions and treatments
  5. Input on public policy
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5
Q

Assumptions of Epidemiology

A
  1. Human disease does not occur at random, factors increase or decrease likelihood of disease
  2. Factors can be identified by systematic investigation of populations
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6
Q

Determinants

A

Factors that change a person’s health or make a difference in health (exposures)

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7
Q

Endemic

A

disease regularly found among a population in a certain area

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8
Q

Epidemic

A

Occurrence of disease in excess of normal expectancy

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9
Q

Pandemic

A

Epidemic occuring worldwide, or crossing international boundaries

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10
Q

Epidemic Intensity

A

(# of deaths / (Global population + Epidemic duration)

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11
Q

Sequence of Epidemiological Investigation

A

–> Suspect Exposure influences disease occurence –> Form hypothesis about exposure-disease association –> Conduct epidemiological studies to measure relationship –> Judge whether association is valid –> Evaluate preventions and treatment –>

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12
Q

Descriptive Epidemiology

A

Analysis of dease patterns according to characteristics of person, place, and time

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13
Q

Types of Epidemiology

A
  1. Descriptive

2. Analytic / Scientific

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14
Q

Roles of Descriptive Epidemiology

A

Describe disease patterns
1. Monitor the publics health
2. Evaluate success of intervention programs
3. Generate hypothesis
Studies: (Case Report, Case Series, Cross-Sectional, Ecologic Study)

Limitation: Cannot Uncover Cause of Disease

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15
Q

Roles of Analytical Epidemiology

A

Search for Disease Causes and Preventions
1. Evaluate hypothesis about causes of disease
2. Evaluate success of intervention programs
Studies: (Clinical Trial, Experimental Study, Case-Control, Cohort)

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16
Q

Person

A 
Permanent Characteristics
- Age, Sex, Race
Biological Characteristics, 
- Immune status, etc.
Acquired Characteristics 
- Marital Status
Activities
- Occupation, Leisure, Medications, Drugs
Conditions Under which one lives
- SES
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17
Q

Person: Marriage

A

Protective Hypothesis - Marriage provides an environment conductive to health

Selective Hypothesis - people who marry are healthier than people who never marry

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18
Q

Place

A

Benefit: Can help us determine where diseases are occuring and if frequency varies by location

What is it?

  • Residency, site of employment, school district, birthplace, etc.
  • Suburban, Urban, Rural

Can determine if certain communities are at an increased risk of disease

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19
Q

Time

A

Occurrences of disease change over time, some are predictable and others are not

Patterns of disease occurence critical for:

  1. Monitoring disease occurrence in a community
  2. Assessing whether ph interrventions made a difference
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20
Q

4 Components for Measuring Disease Frequency

A
  1. Population (Which group of people)
  2. Cases of Disease (Numerator)
  3. Size of Population (Denominator)
  4. Time (Be explicit)
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21
Q

Population (Measuring Disease Frequency)

A

Used as the base group from which we count disease frequency

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22
Q

Population at Risk

A

Members of the population who are capable of developing the disease being studied

Does not include:

  1. Those who already have the disease
  2. Those who cannot get the disease
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23
Q

Source Populations

A

a. Fixed Population: Membership defined on the basis of some event, membership is permanent (e.g. People born in 1982, or survivors of Hiroshima)
b. Dynamic Population: Membership is defined by being in a state or condition, membership is transient (e.g. residents of boston, parents of a teenager)

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24
Q

Numerator of all measures of frequency

A

Cases of disease

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25
Disease
Any Health outcome (positive or negative)
26
Methods of Disease Assesment
Clinical records, diagnostic tests, disease registries, surveillance programs, self reports
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Denominator for All Measures
Size of the population Full or sample of population Necessary for comparison of disease across populations
28
Time (Measures of Disease Frequency)
Single Point in Time - At study enrollment, at birth, on a particular date Interval of Time - A period of follow-up, from birth to 10 years of age
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Types of Measures
Ratios, Proportions, Rates
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Count
The number of cases of a disease or other health phenomenon being studies
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Ratio
Definition: Division of one number by another E.g. Ratio = (Observed number of AIDS cases in country A during june) / (Expected number of AIDS cases in country A during June)
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Proportion
Definition: Division of two related numbers, (the numerator is a subset of the denominator) Often expressed as a percentage
33
Rate
Definition: Division of one number by another in which TIME is an intrinsic part of denominator E.g: Breast cancer incidence rate - number of new cases of breast cancer among 100,000 women over a one year period - 125 cases/100,000 women per year OR 125 cases / 100,000 woman-years
34
Epidemiological Measures of Disease Frequency
Three Types: 1. Prevalence 2. Cumulative Incidence 3. Incidence Rate All measures share three characteristics: Number of cases (numerator), size of population (denominator), Measure of time
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Prevalence
Definition: Measure presence of EXISTING CASES of a disease in a population during a specified time period - A snapshot describing the burden of disease - Involves being in a specific state Denominator includes the TOTAL POPULATION Proportion of population who have disease
36
Point Prevalence
Proportion of population that has the disease at a single point in time Prevalence = (# of Existing cases at a time point) / (# in total population at a time point) Relevant time period does not appear in formula but must be stated using words
37
Incidence
Definition: Measures occurrence of new cases of disease in a population during a specified time period - Involves a TRANSITION from one state to another Denominator only includes population at risk - Exclude those who already have the disease - Exclude those who are immune
38
Prevalence vs. Incidence
Prevalence Incidence What: Existing Disease. New Disease Why: 1. Asses burden of disease. 1. Etiologic research 2. Use when incidence hard. 2. Evaluation of preventions/treatments
39
Cumulative Incidence
- Time is described in words - Measures occurrence of new cases of disease in a population during a specified time period Critical Assumption: All people in the population have been followed for the entire time period (NO LTF) - CI = (# New cases during time period) / (# in population at risk at start of time period)
40
Incidence Rate
- Time is an intrinsic part of denominator - Measures SPEED at which NEW CASES of disease occur in population - Does not assume no LTF - Time is intrinsic part of denominator - Formula: IR = (# New cases during time period) / (Total person-time of observation in population at risk) - Units = Person time
41
Attack Ratio (Incidence Measure)
Proportion of individuals exposed to infectious agent who become infected over a certain time period
42
Case Fatality Ratio (Incidence Measure)
Proportion of individuals with a disease who die of that disease
43
Limitations of Cumulative Incidence
No LTF | - Not a perfect measure in a dynamic population or a fixed population that loses members over time
44
Person Time
Amount of time each person at risk is under observation - Accrued only among persons at risk - Accrued only while being followed Ends when: - Person is no longer part of population at risk - Observation periods end
45
Converting B/w Prevalence & Incidence Rate
Formula: P = IR * D D = average duration of disease Assumption - Population is in a steady state (In = out) - Prevalence is low (<10%)
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How/Why Do We Compare Measures of Disease Frequency?
How: Exposure Status Why: If disease occurs more often or less often in one group than in the other, then there is an association b/w exposure and disease
47
Comparisons
Index group (Exposed) vs. Comparison/Reference Group (Unexposed)
48
Measures of Association
Definition: Comparisons of measures of disease frequency Approaches 1. Absolute 2. Relative
49
Absolute Measure
Def: Calculate the difference b/w two measures of disease frequency Types: 1. Prevalence Difference 2. Risk Difference 3. Rate Difference Formula: RD = R_E - R_U
50
Relative Measure
Def: Calculate the ratio of two measures of disease frequency Types: 1. Prevalence Ratio 2. Risk Ratio 3. Rate Ratio Formula: RR = R_E / R_U
51
Prevalence Differennce
(Based on Prevalence) Def: Difference in prevalence b/w index and comparison groups Formula: PD = P_E - P_U (No units)
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Risk Difference
(Based on Cumulative Incidence) Def: Difference in cumulative incidence b/w index and comparison groups Formula: RD = CI_E - CI_U (No units)
53
Rate Difference
(Based on Incidence Rate) Def: Difference in incidence rate b/w index and comparison groups Formula: RD = IR_E - IR_U (Person Time)
54
Interpreting Absolute Measures of Association
RD = Difference comparison of prevalence/risk/rate of disease in the exposed group to that of unezposed Note: - Focus on the excess disease in exposed grroup - Specify comparison group - Specify time period
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Prevalence Ratio
(Based on Prevalence) Def: Ratio of prevalence b/w index and comparison groups Formula: PR = P_E / P_U (No units)
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Risk Ratio
(Based on Cumulative Incidence) Def: Ratio of cumulative incidence b/w index and comparison groups Formula: RR = CI_E / CI_U (No units)
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Rate Ratio
(Based on Incidence Rate) Def: Ratio of incidence rate b/w index and comparison groups Formula: IRR = IR_E / IR_U (No Units)
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Relative Risk
Generic term repersenting all relative measures of association
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Interpreting Relative Measures of Association
Relative Risk = Ratio comparison of prevalence/risk/rate of disease in the exposed to that of the unexposed group E.g. if RR = 7.45 - Women with ___ were 7.45 x as likely to have __ over a __ year period compared to women without ___ - Or had 7.45 x the risk of ___
60
Excess Relative Risk
(RR-1) x 100% Can be negative
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Risk Difference vs. Relative Risk
RD : Repersents measure of public health impact of exposure on disease occurence RR: Repersents measure of strength or magnitude of the association
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Association
- An identifiable relationship b/w expsure and disease - Indicates that the exposure might cause disease - Comparisons of risk or rates yields an association
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Outbreak Investigation Sequence
1. Confrm 2. Describe 3. Determine the Cause 4. Control
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Outbreak Investigation Detailed
1. Confirm that there is an outbreak 2. Formulating case definitions 3. Conducting case confirmation 4. Establishing the descriptive epidemiology of the outbreak cases 5. Generating and testing hypothesis about the causes of the outbreak 6. Collecting and testing environmental samples 7. Implementing control measures 8. Interacting with the press and public to disseminate information
65
Epidemic Curves
- Used to describe outbreaks - Plot date or time of illness on x-axis, number of cases on y-axis - Tell us: distribution of cases over time, outbreaks magnitude, pattern of spread, time of exposure, shape tells us about mode of transmission
66
Point Source Outbreak
- Persons are exposed over a brief time to the same source Number of cases rises rapidly to peak and then falls gradualy Most cases within one incubation period
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Continuous Common Source Outbreak
- Persons exposed to the same source but exposure is prolonged over a period of time - # of cases might peak and fall, but all cases do not fall within a single incubation
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Propogated Outbreak
- There is no common source, outbreak is person to person | - Curve will cycle through progressivley taller peaks that are often one incubation period apart

Introduction to Epidemiology (1 decks)

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