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Epidemiology and Biostatistics > Cohort Studies > Flashcards

Cohort Studies Flashcards

1
Q

Definition of cross sectional studies

A

Exposure status and disease status of an individual are measured at 1 point in time

Compared to those without disease/different exposure levels

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2
Q

Definition of prevalence ratio

A

Prevalence of disease in exposed divided by prevalence of disease in unexposed

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3
Q

Definition of odds

A

Odds that a diseased person was exposed or unexposed

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4
Q

Definition of odds ratio

A

Ratio of prevalence odds in exposed to prevalence odds in unexposed

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5
Q

Definition of risk

A

Probability of occurrence of disease in a disease free population during a specified time period

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6
Q

Definition of incidence rate/density

A

How rapidly cases occur

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7
Q

Definition of incidence proportion/cumulative incidence

A

No of cases at the end of the given period

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8
Q

Definition of survivor bias

A

Selection bias where results of the survivors of an outcome are disproportionately evaluated
Those who didn’t survive are ignored

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9
Q

Definition of selection bias

A

Bias introduced by selection of individuals so sample obtained is not representative of the whole population

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10
Q

Definition of sampling bias

A

Not all populations represented in the sample

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11
Q

Definition of ascertainment bias

A

People know what group they are in

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12
Q

definition of participation bias

A

Participant acts in a way that they think the researcher wants them to act

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13
Q

Definition of misclassification bias

A

People have been assigned to the wrong groups

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14
Q

Definition of ecological fallacy

A

The results of 1 person assumed to be true for the whole grou[

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15
Q

What are cross sectional studies
What groups are compared
When are these studies used

A

Exposure status and disease status of individual ensured at 1 point in time
Disease prevalence in those with and without exposure/at different exposure levels are compared

Used in health planning

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16
Q

What are the 3 ways of analysing the data in a cross sectional study

A

2x2 tables developed and measures calculated

Calculate
-prevalence ratio (prevalence of disease in exposed/prevalence of disease in unexposed)

  • odds (disease exposed)x(no disease unexposed)/(disease unexposed)x(no disease exposed)
  • odds ratio
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17
Q

How do you interpret the prevalence ratio

A

People with (condition) are (prevalence ratio) more likely to be infected with (disease) than people without (condition)

18
Q

How do you interpret the odds ratio

A

Odds that a person with (disease) is (odds ratio) more/less likely to have (condition) than than those without the (disease)

19
Q

What are the 5 advantages of a cross sectional study

A 
Quick and easy
Data collected once
Measure prevalence for many factors
Multiple outcomes and exposures
Can generate many hypotheses
20
Q

What are the 6 disadvantages of cross sectional studies

A

Difficult to determine time order
Unsuitable for rare diseases (sample size too small)
Reflects determinants of survival and etiologies
Can’t measure incidence
Hard to interpret results
Susceptible to bias

21
Q

What are cohort studies

A

Prospective follow up studies

A group of people who share a common experience/condition are followed up to determine disease incidence

22
Q

How would you use cohort studies to investigate etiologies

A

Study risk factors for developing disease

  • behavioural
  • occupational
  • environmental
23
Q

How would you use cohort studies in prognoses

A

Factors that predict mortality or disability
Factors that alter health outcomes
-treatments
-study of those diagnosed with a disease

24
Q

What are the 3 assumptions made in a cohort study

A

Representative of population
Absence of exposure well defined
Comparability of outcomes

25
Q

What are the 3 types of cohort study

A

Prospective
Retrospective
Ambidirectional

26
Q

What are the 3 main characteristics of a prospective cohort study

A

Identifies population and exposure status
Follows up for disease development
Completion of study takes a long time

27
Q

What are the 4 main characteristics of a retrospective study

A

Existing data identifies exposure status
Identifies present disease status
Short time to assemble study population
Determine disease at present

28
Q

What are the 4 main characteristics of an ambidirectional study

A

Existing data identifies population and exposure
Follow up into future for disease
Short time to assemble study population
Additional time to follow disease development

29
Q

How would you calculate risk and the risk ratio

A

Probability of occurrence of disease free population during specified time period

Risk = new cases over time period/population initially at risk

Risk ratio = risk in exposed/risk in unexposed
=a/(a+b) / c(c+d)

30
Q

How do you interpret risk in cohort studies

A

Over a (time period), (no of new cases) out of (population initially at risk) at risks persons developed the disease

31
Q

How do you calculate the rate and rate ratio in cohort studies

A

Measures the frequency of new cases
Can account for changes in population size (use midpoint population)

Rate = new cases in a population in a time period/total no of person years

Rate ratio = rate in exposed/rate in unexposed

32
Q

What is the difference in incidence rate and incidence proportion

A

Incidence rate
-how rapidly cases occur

Incidence proportion
-no of cases at the end of the given period

33
Q

How would you interpret the relative risk figures

A

=1
-no association

> 1
-Risk in exposed > risk in unexposed (risk factor)

<1
-Risk in exposed < risk in unexposed (protective factor)

34
Q

What are the 5 advantages of cohort studies

A
  • Temporal sequence between assumed cause and outcome
  • Can investigate many outcomes associated with 1 exposure
  • valuable in study of rare exposure
  • reduce risk of survivor bias
  • allow calculation of incidence rates, RR, CI
35
Q

What are the 4 disadvantages to a cohort study

A
  • Inefficient for rare diseases (can take a long time to develop)
  • Require large populations
  • Loss to follow up
  • Expensive and time consuming
36
Q

What are the 3 main types of bias in cohort studies

A

Selection bias
Information bias
Other

37
Q

What are the 3 sources of selection bias

A

Sampling bias
Ascertainment bias
Participation bias

38
Q

Wat are the 2 forms of information bias

A

Misclassification bias

Ecological fallacy

39
Q

What are the 2 other sources of bias

A

Confounders

Chance

40
Q

What 6 factors should you consider in an evaluation of association

A

Temporal sequence
Strength and consistency of association
Dose response relationship
Biological plausibility

Bias

  • Amount of selection bias
  • Completeness of follow ups
  • assessed and controlled for confounders
  • sample size

Epidemiology and Biostatistics (16 decks)

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