HaDPoP general Flashcards
What is a consensus useful for?
- Allocation of resources
- Projections of populations
- Trends in populations Eg Ethnicity or age
How are confidence intervals calculated?
Lower bound = Value ÷ Error factor
Upper bound = Value x error factor
(error factor equation given in exam)
Cohort studies can either be?
1) Prospective - disease free individual recruited and followed up
2) Retrospective - Disease free individuals recruited then exposure status calculated from historical documentation and followed up
Explain internal comparisons
Occur when you have sub-cohorts within your original group and then compare exposed and unexposed within the cohort
Use IRR
Explain external comparisons
Occur when you have your exposed population compared against a reference population instead
Use an SMR calculation (removes confounders)
Describe healthy worker effect
Healthy worker effect is whereby there is biasing of results when a study involves workers / employed individual compared ti a reference population and is a form of selection bias
When a comparison is made, it should always be against other working individuals to prevent any bias
Describe a case control study
A case-control study involves recruiting disease-free (controls) individuals and diseased individuals (cases) and then their exposure status is determined
What biases affect case-control studies?
- Selection bias
- Recall bias
What are the positives and negatives of a cohort study?
+ Good to study rare EXPOSURE; adequate numbers of people can be picked from the population, where a small number is exposed
+ Opportunity to look for different potential OUTCOMES at once from varying exposures
- Expensive and time consuming, especially if the disease has a long latent time period Eg AIDS
+ Allows for calculation of specific absolute risk
What are the positives and negatives of a case-control study?
+ Good for rare diseases; no need to follow thousands of individuals to get a few cases
+ Opportunity to look for different potential EXPOSURES at once, as long as detailed background can be obtained
+ Cheap and quick
- Can not obtain absolute risk (unless nested case-control)
- Heavily affected by recall and selection bias
Why do randomised controlled trials use randomisation?
Remove any confounders that may be present in the study, known or unknown
What is the Bradford-Hill Criteria used for?
To determine whether a causal-effect relationship has been established (once confounders, bias and chance have been removed), Bradford-Hill criteria can be used to evaluate the relationship
The more Bradford-Hill criteria present, the more likely it is to be a causal-effect relationship
What are the 9 Bradford-hill criteria
1) Strength of association
2) Specificity of association
3) Consistency of association
4) Temporal sequence
5) Dose response
6) Reversibility
7) Biological Plausibility
8) Coherence of theory
9) Analogy
Bradford-Hill criteria. Strength of association
Stronger associations (Eg high IRR or OR) are more likely to be causal
Bradford-Hill criteria. Specificity of association
Outcome is associated with a specific factor
Eg mesothelioma caused by asbestos exposure
