Evidence for population health Flashcards
Define: Epidemiology
Determinants + distribution of disease + death
What are the pros of anecdote + case series?
- Quick
- Easy to perform in clinic
- Provides new unobserved conditions
- Provides new potential risk factors
What are the cons of anecdote + case series?
- Not scientific (can’t test a hypothesis)
- Seriously affected by observer bias
- Difficult to make inference about disease cause
What is a cross-sectional survey?
- A snapshot of people with an outcome
- Count the number of people with a disease in a short time period in a pre-defined population
What are the pros of a cross-sectional survey?
- Quick
- Good at estimating prevalence of the disease and the burden
What are the cons of a cross-sectional survey?
- Only represents that point in time
- Cannot estimate incidence of disease
- Sampling frame may lead to bias
Define: Prevalence
Cases of disease that are present in the group
Define: Incidence
New cases of disease
How is incidence measured?
- A register is used
- Record new cases in a pre-specified population
What is a counterfactual method?
Would the disease have happened at the same time in the same person if the factor was not present?
This is not a practical method for answering the cause of the disease
What are the pros of ecological studies?
- Cheaper
- Less prone to bias due to participation
- Easy to perform using routinely collected data
- Provides new hypotheses about the causes of a disease or condition
- Provides new potential risk factors
What are the cons of ecological studies?
- Ecological fallacy - do population-level measures hold for the individual?
- Assume average value of risk factor applies to all individuals
- Assume average incidence applies to all individuals
- Data collection may vary
Describe: case-control study
Case = someone who has the disease Control = someone who does not have the disease
They are compared for an exposure
It is retrospective (i.e. after the disease has been diagnosed)
What are the pros of a case-control study?
- Good for rare disease/exposures
- Fairly quick since no need to follow-up
What are the cons of a case-control study?
- Prone to selection bias
- Prone to participation bias
- Finding a suitable control group can be difficult
- Difference in recall leading to bias
Describe: Cohort study
- Start with a population with no people diagnosed with the disease
- Look at who is exposed/not
- Look at rate of outcome for disease
Define: cohort
People who share a common experience or condition e.g. smokers, birth cohort
What are the pros of a cohort study?
- Good for rare exposures
- Can look at multiple outcomes
- Reduces information bias
- Direct measure of incidence
What are the cons of a cohort study?
- Inefficient for rare diseases
- Expensive
- Retrospective is quicker
- Loss to follow-up
Describe: randomised control trial
GOLD-STANDARD
Study population = health people for preventative trial OR sick people for therapeutic trial
Study population is assigned randomly to treatment/control group
Control group does not receive treatment
Follow the groups through time + look at rates of outcome
What are the pros of a randomised control trial?
- Strongest evidence for causality
- Selection bias removed
- Observer bias removed
What are the cons of a randomised control trial?
- Not real life
- High cost
- Unethical for many research questions
What are the different types of blinding in a randomised control trial?
- Patient doesn’t know if they are having the treatment or not
- Clinical doesn’t know what the patient is having
- Analyst doesn’t know what drug A or drug B are
Describe: intention to treat analysis
Assuming that every person follows their part of the randomised control trial correctly + analyses the data as if the patient did the therapy for the whole trial
Makes it the best representative of real life
Define: Error
The difference between an estimated/measured value and the true value
Give potential sources of error
- Study design
- Sample collection
- Lab analysis
- Data analysis
- Data management
- Data collection
Define: diagnostic bias
When diagnosis is made based on exposure
Give examples of: self-selection bias
- Participants contacting the study through adverts
- Some people are more likely to participate due to family history
Define: information bias
Bias arising from measurement error
What types of bias are included in information bias?
- Recall bias
- Interviewer bias
- Surrogate bias
When does misclassification bias occur?
When data is placed in categories
