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PUBH 4040 > 7: Cohort Study Design > Flashcards

7: Cohort Study Design Flashcards

1
Q

Temporality

A

refers to the timing of information about cause and effect. demonstrating temporality is a difficulty of most observational studies

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2
Q

Cross-sectional and case-control study designs are based on exposure and disease information that is collected at the same time. Advantage? Disadvantage?

A

Advantage: efficient for generating and testing hypotheses
Disadvantage: leads to challenges regarding interpretation of results

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3
Q

Limitations of Study Designs of Cross-Sectional, Ecologic, and Case-Control (2)

A
  1. No actual lapse of time between measurement of exposure and disease
  2. not well suited for uncommon exposures
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4
Q

cohors

A

referred to one of ten divisions of an ancient Roman legion

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5
Q

cohort

A

a population group, or subset thereof, that is followed over a period of time

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6
Q

cohort group members experience a common exposure:

A
  1. associated with a specific setting

2. share non-specific exposure associated with a general classification (birth cohort)

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7
Q

birth cohort

A

being born in the same year

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8
Q

Cohort Effect

A

the influence of membership in a particular cohort (less than 5% population smoked in early 1900s > free cigs for WW1 troops > shift in distribution of age of onset of lung cancer)

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9
Q

Cohort Analysis

A

the tabulation and analysis of morbidity or mortality rates

  • with relationship to ages of a specific cohort identified
  • with respect to a particular period of time
  • followed as they pass through different ages during part or all of their life span
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10
Q

Wade Hampton Frost

A

Arranged tuberculosis mortality rates in a table with age on one axis and year of death on the other. Drew substantial attention to the cohort analysis method.

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11
Q

Life Table Methods

A

Give estimates for survival during time intervals and present the cumulative survival probability at the end of the interval. Can be constructed to portray the survival times of patients in clinical trials.

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12
Q

Two Life Table Methods

A
  1. Cohort Life Table

2. Period Life Table

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13
Q

Cohort Life Table

A

shows the mortality experience of all persons born during a particular year

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14
Q

Period Life Table

A

enables us to project the future life expectancy of persons born during the year as well as the remaining life expectancy of persons who have attained a certain age

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15
Q

Years of Potential Life Lost (YPLL)

A

computed for each individual in a population by subtraction that person’s life span from the average life expectancy of the population

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16
Q

Disability-Adjusted Life Years (DALYs)

A

adds the time a person has a disability to the time lost to early death

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17
Q

Survival Curves

A

method for portraying survival times

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18
Q

required info in order to construct a survival curve (3)

A
  1. time of entry into the study
  2. time of death or other outcome
  3. status of patient at time of outcome (dead or censored (lost to follow-up))
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19
Q

inverse of survival curve

A

lethality curve. useful for insecticides, etc.

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20
Q

Cohort Study

A
  • Guided by scientific question, not availability of group for study.
  • start with group of subjects who lack a positive history of outcome of interest and are at risk for the outcome.
  • Includes at least two observation points: (1) exposure status and eligibility, (2) determine number of incident cases
  • permit calculation of incidence rates > risk rates
  • collection of primary data (initial exposure data)
  • involve comparison of disease rates between exposed and non-exposed groups
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21
Q

Cohort studies differ according to:

A

sampling strategy used. population-based vs. exposure-based

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22
Q

Population-Based Cohort Study

A

cohort includes either an entire population or a representative sample of the population. exposures unknown until first period of observation when exposure information is collected. two or more levels of exposure. not efficient for rare exposures.

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23
Q

Framingham Study

A

Population-Based. ongoing study of CHD. used random sample of town from targeted age range (not entire town population)

24
Q

Tecumseh Study

A

Population-Based. total community cohort. examined contribution of environmental and constitutional factors to maintenance of health and origins of illness

25
Q

Levels of exposure

A
  • Dichotomous variable (exposed vs. nonexposed)

- Continuous variable (blood pressure measurement)

26
Q

Exposure-Based Cohort Study

A

made up of subjects with a common exposure. GREAT FOR RARE EXPOSURE! certain groups may have higher exposures than general population to specific hazards

27
Q

Comparison (Non-Exposed Group)

A

similar in demographics and geography to exposed group, but lacks the exposure. in occupational setting, several categories of exposure may exist (physician vs. billing staff)

28
Q

Outcome Measures

A
  • Discrete Events (single events and multiple occurrences)
  • Levels of Disease Markers
  • Changes in Disease Markers (rate of change)
29
Q

Prospective Cohort Study

A

determination of exposure levels (present) and follow-up for occurrence of disease (future)

30
Q

EXAMPLE: The National Children’s Study

A

Prospective Cohort

31
Q

Prospective Cohort Advantages

A
  • enable investigator to collect data on exposures; MOST DIRECT and specific test of study hypothesis
  • size of cohort under greater control by investigators, recruit more individuals if needed
  • biological and physiological assays can be performed with decreased concern that the outcome will be affected by the under lying disease process (blood sample, lung function)
  • direct measures of environment can be made
32
Q

Prospective Cohort Disadvantages

A

expensive and labor intensive, have to wait for cases to accrue

33
Q

Retrospective Cohort Study

A

make use of historical data to determine exposure level (past) and collect occurrence of disease (present)

34
Q

How is retrospective cohort different than a case-control

A

dont know who will get disease, case-control does

35
Q

Retrospective Cohort Advantages

A
  • significant amount follow-up accrued in short period of time
  • extensive amount of exposure data collected and available at minimal cost
36
Q

Retrospective Cohort Disadvantages

A

cant recall exposure, or cant access exposure data

37
Q

Historical Prospective Cohort Study

A

makes use of both retrospective features ( to determine baseline exposure, past and present) and prospective features (to determine disease incidence, future).

38
Q

Ambispective Cohort Study

A

another term for Historical Prospective

39
Q

Practical Considerations Regarding Cohort Studies (5)

A
  1. Availability of exposure data
  2. size and cost of the cohort used
  3. Data collection and data management
  4. Follow-up issues
  5. Sufficiency of scientific justification
40
Q
  1. Availability of Exposure Data
A

High quality historical exposure data are absolutely essential for retrospective cohort studies

41
Q
  1. Size and Cost of the Cohort Used
A

The larger the size of the cohort, the greater the opportunity to obtain findings in a timely manner. Resource constraints typically influence design decisions

42
Q
  1. Data Collection and Data Management
A

Explicit protocols for quality control. organizational and administrative burdens increased with multiple levels of data collection

43
Q
  1. Follow-up Issues
A

cohorts only effective with follow-up. Active vs. Passive follow-up

44
Q

Active Follow-up

A

investigator obtains data through direct contact with cohort

45
Q

Passive Follow-up

A

record linkage between databases. data collected and maintained by organizations outside investigative team.

46
Q
  1. Sufficiency of Scientific Justification
A

need considerable scientific rationale for cohort study.

47
Q

cohort studies are the only observational study design that…?

A

permits examination of multiple outcomes

48
Q

Relative Risk

A

direct measure of association between exposure and outcome. [A/A+B]/[C/C+D] Exposure > Result

49
Q

Attributable Risk

A

“Risk Difference” [A/A+B]-[C/C+D] great for occupational health

50
Q

RR=1

A

risk (rate) of disease among exposed is no different from risk of disease in non-exposed

51
Q

RR>or =2

A

risk is twice as high

52
Q

RR<or=0.5

A

protective factor, exposure associated with half the risk of disease

53
Q

Nested Case-Control Studies

A

type of case-control study in which cases and controls are drawn from the population in a cohort study

54
Q

Nested Case-Control Advantages

A
  • degree of control over confounding factors

- reduce cost because exposure information is collected from subset of cohort only

55
Q

Advantages of Cohort Studies

A
  • direct determination of RISK
  • TIME SEQUENCING of exposure and outcome
  • can study MULTIPLE OUTCOMES
  • can study RARE EXPOSURES
56
Q

Limitations of Cohort Studies

A
  • take a LONG TIME
  • COSTLY
  • SUBJECTS LOST to follow-up

PUBH 4040 (12 decks)

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