Cohort Studies Flashcards
Cohort study definition
Cohort studies define and measure the risk factor and then evaluate the outcome in a suitable demographic group over time (you get to pick the people), outcome can be the presence or absence of disease associated with a single RF (not multiple)
What is a major difference between Cohort and CCS?
Cohort studies have a well defined population in demographics and numbers. Bias and confounding controlled better
What are the two types of cohort studies?
prospective and retrospective
What is usually done before a cohort study?
a case control study
What is ideal for the control group?
It is ideal for the control group to have no exposure to the RF. Best if personal interviews are performed. Can be complicated if using published data or environmental RF.
What is the key point for Cohort studies?
Presence or absence of risk factor is determined before outcome occurs
How do you calculate risk?
a/(a+b)
How do you calculate relative risk?
a/(a+b) / c(c+d) =
How do you form a 2x2?
Risk factor on side and Disease on top
What does a RR of 6 tell you?
6x more likely to get disease if exposed
Odds Ratio calculation
(a/c) / (b/d), include an error factor
Person Years
This adjusts for the amount of time that any individual member of the cohort’s data is available; some in study longer, evaluate number of person years instead of number of people
Confounding in Cohort studies
Associations between risk factors and cardiovascular disease outcomes are confounded by pre-existing cardiac, renal and other diseases
Bias
Anything that might negatively affect the representativity of the cohorts studied
Information bias
Is information about outcome obtained in the same way for those exposed and those not?
Features to look for in cohort studies
- What steps were taken to minimize information bias?
- How complete was the follow up in both groups?
- Were potential confounding factors sought and controlled for in the analysis?
Cohort vs Case study
Long term and require a lot of planning, less useful in study of diseases of low prevalence or exposure, deals better with confounding and bias, strength of association of RR stronger than OR
Why can you extrapolate the results in a case control study?
the demographic latitudes inherent in control group formation and the additional variation built into the confidence interval by including factorials for control groups
Clinical trials
A cohort study in which the exposure to the effector is controlled. (Placebo controlled, single/double/triple blind)
Triple blind experiment
Patient, clinician, and lab analyzing does not know groups
Diagnosis can be made through?
quantitative or qualitative, subjective or objective methods: serology assays, PCR, X-Ray, CAT scans, experience
2x2 Table for test sensitivity and specificity
side has test positive and negative; top has disease positive and negative
How to calculate sensitivity from 2x2?
a / total disease positives
How to calculate specificity from 2x2?
d / total disease negatives
