Public Health 2 Flashcards
What is a case control study
- Looks at 2 sets of participants. One group has the condition you are interested in (the cases) and one group does not have it (the controls).
What are the advantages of a case-control study ?
- Good for rare outcomes e.g. cancer
- Quicker than cohort or intervention studies as outcome has already happened
- Can investigate multiple exposures
What are the disadvantages of a case-control study ?
- Difficulties finding controls to match cases
- Prone to selection bias
What is a cohort study ?
- Participants who do not have the outcome at baseline are followed over time to estimate the incidence of the outcome.
What are the advantages of a cohort study ?
- Can follow-up a group with a rare exposure e.g. natural disaster
- Good for common or multiple outcomes
- Less risk of selection and recall bias
What are the disadvantages of a cohort study ?
- Take a long time
- Loss to follow up
- Need a large sample size
Cross-Sectional Studies
- Observational studies that analyse data from a population at a single point in time
- What are the advantages of a cross-sectional study ?
- Relatively quick and cheap
- Provide data on prevalence at a single point in time
- Large sample size
- Good for surveillance and public health planning
What are the disadvantages of a cross sectional study ?
- Risk of reverse causality
- Cannot measure incidence
- Risk recall bias and non-response
What is a randomised control trial ?
- Gold standard trial
- A trial in which subjects are randomly assigned to one of two groups: one (the experimental group) receiving the intervention that is being tested, and the other (the comparison group or control) receiving an alternative (conventional) treatment.
What are the advantages of a randomised control trial ?
- Low risk of bias and confounding
What are the disadvantages of a randomised control trial ?
- Time consuming and expensive
- Specific inclusion/exclusions criteria may mean the study is different from typical patients e.g. excludes elderly
How can an association between 2 things be explained ?
- Chance
- Bias
- Confounding
- Reverse causality
- A true causal association
Selection bias can result from
- Selection of study participants
- Allocation of participants to different study groups
How can the selection of study participants and there allocation to different study groups impact selection bias ?
- Non response e.g. are those who don’t respond likely to be from a specific group e.g. elderly
- Loss to follow up e.g. are those who drop out more likely to be better or worse ?
- Are those in the intervention group (or the cases) in some way from the controls other than the exposure in question
What types of information bias are there ?
- Measurement
- Observer
- Recall Reporting
What types of Bias are there ?
- Information
- Selection
- Publication
What is publication bias ?
- Not all trial results are published
- Papers with less positive results are less likely to be published
What is confounding ?
- A situation in which estimates between an exposure and outcome is distorted because of the association of the exposure with another factor (confounder) that is also independently associated with the outcome
- E.g. More shark attacks while there are more ice cream sales
Reverse causality
- Refers to the situation when an association between an exposure and an outcome could be due to the outcome causing the exposure rather than the exposure causing the outcome
What is the Bradford-Hill Criteria for Causality
- List of things required to say that one thing causes another
Features of the Bradford Hill Criteria
- Strength
- Consistency
- Dose-response
- Temporality
- Plausibility
- Reversibility
- Coherence
- Analogy
- Specificity