35 - Aetiology and Risk Factors for CVD Flashcards
Two broad types of research questions
1) Descriptive (EG: how common is coronary heart disease?)
2) Analytical (EG: does dyslipidaemia increase risk of CHD?)
Examples of descriptive studies
1)
2)
3)
1) Case studies, reports
2) Ecological studies
3) Cross-sectional
Examples of analytical studies
1)
2)
3)
1) Case-control studies
2) Cohort studies
3) Clinical trials (interventional)
Longitudinal vs non-longitudinal studies
Longitudinal studies involve following subjects over time. Non-longitudinal studies only give data on one point in time
Examples of non-longitudinal studies 1) 2) 3) 4)
1) Case-studies
2) Ecological reports
3) Cross-sectional studies
4) Case-control studies
Examples of longitudinal studies
1)
2)
1) Cohort studies
2) Clinical trials
Prevalence
Number of existing cases of outcome of interest at a point in time in a defined population
How is prevalence expressed?
As a proportion or percentage
Examples of prevalence
1)
2)
3)
1) Percentage of Australians who smoke
2) Percentage of 65 year-old Australians with coronary heart disease
3) Percentage of these who smoke
Incidence
Number of new cases of outcome of interest in a defined population, observed over a defined period
How is incidence expressed?
As a proportion
Only source of data for calculating incidence
Longitudinal studies
Examples of incidence
1)
2)
1) Number of Australians who started smoking in 2014
2) Number of 65 year old males who began smoking in 2014
Common measurement of incidence
Number of outcomes of interest/1000 people per year
Risk
Probability of disease occurring in a disease-free population during a specified time period
How is risk calculated?
N/P
N = number of new cases in a defined period
P = population at risk
Issue with risk
P = population at risk assumes that all subjects were measured for equal periods of time.
EG: in 1995, 3 cases of lung cancer developed out of 1000
men; risk = 3/1000 per year.
This assumes that all 1000 men were followed for the entire year, which is not necessarily the case.
Rate
Probability of disease occurring in a disease-free population during the sum of the individual follow-up periods
Benefits of rate
1)
2)
1) Takes into account different measurement times for subjects.
2) Recruitment of subjects can be staggered. Each subject can have a different baseline time.
Hazard
1)
2)
3)
1) Special kind of rate that is continuously updated as a longitudinal study progresses.
2) Is an instantaneous rate - applies to one particular point in time.
3) Derived from longitudinal studies
Absolute risk/rate
Isolated measurement of risk/rate.
Says nothing about association with exposure.
EG: 3/1000 myocardial infarcts/year
Ways to indicate association
Relative risk and attributable risk
Which absolute risk-rate measurements of relative and attributable risks rely on?
1)
2)
1) Risk/rate among exposed
2) Risk/rate among unexposed
Synonyms of relative risk
Risk ratio, rate ratio
What does relative risk describe?
Relative change in magnitude of risk/rate outcome, associated with exposure
How is relative risk calculated?
Rate exposed/Rate unexposed
Attributable risk synonyms
Risk difference, rate difference
What does attributable risk describe?
Absolute magnitude of change in risk/rate outcome, associated with exposure
How is attributable risk calculated?
Rate exposed - rate unexposed
Attributable risk percent
(Rate exposed - rate unexposed / rate exposed) x 100
Gives percentage of incident disease among exposed that can be attributed to exposure.
Rt
Incidence in total population
Population attributable risk
Rt (incidence in whole population) - Ru (unexposed)
Gives excess risk of the outcome in the population due to exposure
Population attributable risk percent
(Rt-Ru/Ru)x100
Proportion of incident disease among whole population that is due to exposure.
Synonym of population attributable risk
Preventable fraction
