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
What are the 3 types of cohort study
Prospective Retrospective Ambidirectional
26
What are the 3 main characteristics of a prospective cohort study
Identifies population and exposure status Follows up for disease development Completion of study takes a long time
27
What are the 4 main characteristics of a retrospective study
Existing data identifies exposure status Identifies present disease status Short time to assemble study population Determine disease at present
28
What are the 4 main characteristics of an ambidirectional study
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
How would you calculate risk and the risk ratio
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
How do you interpret risk in cohort studies
Over a (time period), (no of new cases) out of (population initially at risk) at risks persons developed the disease
31
How do you calculate the rate and rate ratio in cohort studies
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
What is the difference in incidence rate and incidence proportion
Incidence rate -how rapidly cases occur Incidence proportion -no of cases at the end of the given period
33
How would you interpret the relative risk figures
=1 -no association >1 -Risk in exposed > risk in unexposed (risk factor) <1 -Risk in exposed < risk in unexposed (protective factor)
34
What are the 5 advantages of cohort studies
- 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
What are the 4 disadvantages to a cohort study
- Inefficient for rare diseases (can take a long time to develop) - Require large populations - Loss to follow up - Expensive and time consuming
36
What are the 3 main types of bias in cohort studies
Selection bias Information bias Other
37
What are the 3 sources of selection bias
Sampling bias Ascertainment bias Participation bias
38
Wat are the 2 forms of information bias
Misclassification bias | Ecological fallacy
39
What are the 2 other sources of bias
Confounders | Chance
40
What 6 factors should you consider in an evaluation of association
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