Lecture 6 and 7: Evidence for disease prevention Flashcards
What is a descriptive study?
Describe cases (those with the disease) Describe population (persons in whom cases arise) Does not explain causality, used to generate a hypothesis.
What is the purpose of a descriptive study?
To know how much disease a region or group has and to formulate a worthy hypothesis
what is the counterfactual; method
what would have happened if??? would the disease have happened in the same person at the same time? in order to attempt to prove a cause of a disease.
Method 0:
What is an anecdote/case series?
Anedotal
No control/comparison group
cant be used in analytical epidemiology as there is no counterfactual group
Method 1:What is a cross sectional survey?
Snapshot of people with an outcome
Not easy to have a counterfactual
looking at what is happening at the time/now
What is method 2 measuring incidence?
When new cases arise
Can be used in ecological studies
What is method 3 ecological study?
Interested in groups not individuals e.g country level of cancer plotted against fat intake
Observational study-can not manipulate anything
Unit of observation is a group
What is method 4 case control studies?
Cases- have the disease
Controls - don’t have the disease
Ask about exposure
Can calculate odds ratio
Good representation of relative risk
Common disease, cant use odds ratio as it doesn’t properly represent risk
o Doesn’t represent a standard counterfactual – roughly the non-exposed groups in both the ‘cases’ and ‘controls’ groups
What is method 5 cohort study?
Followed through time for the outcome
Nobody has the disease at the start
Measured exposure to plit cohort into exposed and non exposed- follow groups through time
Measure rate of outcome in each group
Counterfactual- people who are not exposed
What is method 6 randomised controlled trial?
Seen as gold standard
Healthy people for preventative trial, sick people for therapeutic trial
randomised as to whether you get treatment or not
follow groups and measure rates of outcome
What are the +ve of method 6?
strongest evidence for causality
if randomised, selection bias and confounding is removed
if blinded, less observer bias
What are the -ve of method 6?
Not real life, high cost, inappropriate/unethical for many research questions
What is blinding?
participants are not aware of which group they are in
What is intention to treat analysis?
At the start of a RCT people are assigned to treatment or control group, data analysed as if they took their treatment even if they withdrew = represents real life
What is error?
difference between estimate/measure value and the true value- impossible to not have error
What is selection bias?
Arises from sample selection, the ignored should be samples e.g prisons, hospitals, babies
What is diagnostic bias?
occurs when made on basis of exposure, make assumptions e.g. doctor may diagnose a mesothelioma because they’ve been exposed to asbestos when it may actually be something else
What is self selection bias?
may come about when subjects make decisions- when patients come forward wanting to be part of a study
What is participation bias?
Cases have a clear motivation for participating as they have disease
What is information bias?
error in the information collected, wrong info on right group of people
What is recall bias?
errors in recall of information, e.g. mothers of children with cancer
What is interview bias?
Participants say what they think the interviewer want to hear
What is surrogate bias?
have to ask a surrogate about an individual e.g. baby, dead person
May not want to answer difficult questions
What is confounding variable?
variables that the researcher fails to control or eliminate, damaging the internal validity of an experiment
