Aetiology & CVD Risk Factors Flashcards
What do population and clinical studies address?
Two broad types of research question.
- Descriptive (ie. how common is CHD?)
- Analytical (cause and effect - ie. does lipidaemia increase the risk of CHD?)
What is the difference between observational studies and interventional studies?
Observational = descriptive Interventional = analytical
What are some of the ways that studies are classified?
Classification can be:
- observation or interventional (O/I)
- descriptive or analytical (D/A)
- longitudinal or non-longitudinal (L/N)
What are some types of observational studies?
Case Studies/Case Reports: O - D - N Ecological Studies: O - D - N Cross-sectional Studies: O - D - N Case-control Studies: O - A - N Cohort Studies: O - A - L Clinical Trials: I - A -L
Describe the different between longitudinal and non-longitudinal studies?
Non-longitudinal studies are ecological, cross sectional and case-control studies and include no follow up study of study subjects. The information is usually collected in only one encounter with those subjects.
Longitudinal studies include cohort studies and clinical trials and involves the following up of study subjects. Information is progressively collected over multiple encounters with study subjects over a period of time. The only studies that allow us to determine risk.
Explain what is meant by RISK and RATE? Give examples.
Risk is the probability of disease occurring in a disease-free population during a specified time period.
RISK = n (new cases in a defined period) / P (population at risk)
For example: in 1995, 3 cases of lung cancer developed out of 1000 men; risk = 3/1000
This assumes that all 1000 men were watched for the whole year however, in reality follow-up periods for individuals may not have been for the full year.
Rate is the probability of disease occurring in a disease-free population during the sum of individual follow-up periods.
RATE = n (new cases in a defined period)/ total person-time of follow up (the sum of fixed time increments for each person)
For example: 3 cases of lung cancer developed out of 1000 person years of follow-up; rate = 3/1000. The denominator makes explicit the time that the population at risk actually spent being at risk.
What does prevalence refer to? Give an example.
It refers to a number of existing cases….
Essentially it is a PROPORTION
Prevalence is the number of existing cases of an outcome of interest (ie. risk factor of disease) in a defined population, at one point/period in time. It is expressed as a proportion or percentage.
For example: % of 65yo Australia males with CVD
Convey the concept of Person-time:
A benefit of using person-time is that it allows for accurate representation of the rate of disease in a population according to the longitudinal data obtained. It also allows for the inconsistency in subject participation. Recruitment of subjects into studies is often staggered and so the baseline for each is different
Explain the term Hazard.
Hazard is a special type of rate that is continuously updates as a longitudinal study progress. It is a rate that applies to an exact point in time: an instantaneous rate. It is derived from longitudinal studies, especially clinical trials, with close follow-up.
Explain associations in epidemiology? Why are associations important?
In epidemiology, studies aim to seek association between 2 or more variables. This is so as to make inferences about cause and effect (exposure & outcome) and correlation
What is the concept of incidence? Give an example.
It is the number of new cases of an outcome of interest arising from a defined population, during a time interval.
It is a RATE
Incidence is the number of new cases of an outcome of interest arising from a defined population during a time interval. It is expressed as a rate (over time) and can only be drawn from longitudinal studies
For example: number of 65yo males who developed CVD in 2012
What is the different between cause & effect and correlations?
Cause and Effect: example: does smoking (exposure) increase the likelihood of CHD (outcome)? by how much?
Correlation: example: does blood pressure increase with age? how quickly?
Discuss the concept of Absolute risk/rate with relative risk and attributable risk?
Absolute Risk/Rate is an isolated measurement of risk/rate. For example: 5 strokes/10,000 men per year. No indication of association with exposure (no indication of causes of strokes)
Relative risk and Attributable risk provide indication of association. They are two ways to describe cause-and-effect relationship between exposure and outcome. Each relies on comparison of 2 (absolute) risk/rate measurements:
- risk/rate among exposed (Re)
- risk/rate among unexposed (Ru)
What is relative risk? (AKA risk ratio/rate ratio)
Relative Risk/Risk Ratio/Rate Ratio = Re/Ru
It indicates the relative magnitude of change in risk/rate of outcome, associated with exposure.
What is attributable risk?
Attributable Risk/Risk difference/Rate difference = Re-Ru
It indicates the absolute magnitude of change in risk/rate of outcome, associated with exposure.
