PHEPB Cohort Studies: evidence on risk factors for cardiovascular disease Flashcards
Describe analytic studies
analytic studies: the observed distribution may be investigated by asking one of three questions:
- do persons with the charactersitic have the disease more frequently than those who do not have the characteristic? (cross-sectional studies)
- do persons with the characteristic develop the disease more frequently than those who do not have the disease? (longitudinal/cohort studies)
- do persons with the disease have a characterstic more frequently than those without the disease? (case-control studies)
Describe the design of an observational cohort / follow up / longitudinal / study
What is the definition of a prospective cohort study?
Observational study (we’re not intervening) where a population is studied for the presence of a fixed or modifiable exposure, which is thought to be a cause of a condition (e.g. CVD), prior to the onset of a condition.
The entire population is followed up in time, and the incidence of disease in exposed individuals is compared with the incidence in those not exposed
Risk factors for CVD?
In studies, you want to try to modifiable risk factors → things we can control
Give an example of an influential cohort study
5200 Adults in Framingham, Massachusettes, in 1950 were examined (without disease) for CVD risk factors (inc BP, cholesterol, smoking, BMI etc.), and reexamined
on a 2 year cycle. 1st and 2nd gen follow up also done.
It developed a Franingham risk score, BUT this tends to overestimate CVD risk if not calibrated to the local population- as it is not representitive of other geo locations
What is QRISK?
- CVD risk score based on 318 GP practices who use QRESEARCH
- Uses age, sex, BP, smoking, Total Chol:HDL, BMI,
FH CVD, Townsend (deprivation of an area), Anti hyp meds. - 1.3 million patients aged 35-74 yrs, 1995-2007, validated in 0.6 million
- Nationally representative, performs better than Frammingham which overestimates by 35%, hence why we use this one
Describe another example of a prospective cohort study
A postal questionnaire sent in 1951 to men and
women on the British Medical Register.
Asked questions on smoking habits. 34,439 male and 6,194 female doctors replied. Rates of
disease (CHD, COPD, Lung Cancer) were compared between smoking groups (to 1991).
What are the main types of study populations?
Describe exposure
Defining exposure
– industrial (rare); vinly chloride, radiation
– infectious; hepatitis B, HIV
– social; stress, social class, community
– non-biological and biological
Degree / duration of exposure
– type of exposure; intermittent, constant
– changes in exposure over time
Retrospective (historical) & prospective ascertainment of exposure
Sources
– medical, employment, union records
– supplied by study subjects
– direct measurement
– ascertained from medical examination,
biological specimens (current or stored)
What are confounding variables?
What is the action on confounders?
What should be aware of when thinking of confounders?
Describe the bias in cohort studies
Losses to follow-up occur in all cohort studies
Reduce power and dilute results
Problematic if more drop-outs in one exposure group compared with another
Very important if drop-out is due to development of disease
Beware of other types of bias, e.g., ascertainment, interviewer, non-response, selection bias
Use this to calculate the relative risk of getting disease upon exposure to the solvent
Using this new info, calculate the relative risk
Describe outcomes and link it with cohort studies
Describe the risk analysis of cohort studies
Calculation of the incidence rate or risk of outcome
in the exposed cohort vs unexposed
Relative risk is measured as a rate or risk ratio
Risk expresses the number of outcomes per recruited study pop
Rate expresses the number of outcomes per person
time of those in the study interval
Absolute excess risk is the risk in exposed persons
minus risk in unexposed
RELATIVE RISK= RISK IN EXPOSED / RISK IN UNEXPOSED
Explain incidence risk vs incident rate
ask rauhaan bc respectly wot the hell
Use this info to calculate relative risk and excess risk
What are the main adv of cohort studies?
Evidence of exposure does not depend on memory (except in historical cohorts)
Exposure is measured before disease onset, reducing potential for bias, and allowing causality to be assumed
Multiple outcomes can be studied for any one exposure
Incidence of disease can be measured in exposed and unexposed groups
Potential for nested case control studies
How would you design a nested case control study?
In a nested case-control study, you would select the controls from the same cohort as the cases, and they would be matched to the cases on certain characteristics such as age, sex, and other relevant factors.
The advantage of a nested case-control study is that it is more efficient than a full cohort study, since you only need to collect data on a sample of the cohort, rather than the entire cohort.
What are the disadvantages of cohort studies?
What was the prospective studies collab?
