Critical Numbers 1 Flashcards
How is a sample described?
Using descriptive statistics
How is inference about population made?
Inferential statistics
What is sampling?
May be randomly or non-randomly selected
Different methods of random and non-random sampling
Sample must represent population of interest
Helps make results generalisable
What is bias?
When certain subgroups from the target population are over/under-represented
Arise when imperfections in the research process cause our findings to deviate from the truth
Can occur in all studies
Can occur intentionally or unintentionally
Impacts upon validity and reliability of study findings
Can distort results
What are the types of bias?
Sampling bias - sample does not represent population of interest
Recall bias - inaccurate recall of past events/exposures/behaviours
Information bias - incorrect measurements e.g. miscalibrated machine
The ‘Hawthorne’ effect - participants change their behaviour when they know they are being observed
Attrition bias - differential dropout from studies e.g. sicker participants drop out so our outcome is only measured on healthier participants
What is confounding?
A form of bias
Confounding variables obscure the real effect of an exposure on an outcome
What is a confounder?
Related to both exposure and outcome
Not on the casual pathway
E.g. a high salt diet can cause high blood pressure which can lead to stroke
So blood pressure is not a confounding factor in the relationship between diet and stroke, rather a mechanism
What are the types of study designs?
Experimental - the researchers have intervened in some way
Observational - the researchers have not intervened, merely observed
What can observational studies be?
Retrospective - looking back into the past
Cross-sectional - a single snapshot in time
Prospective - following up over time
What are randomised controlled trials?
Randomly allocate participants to different interventions and follow up
- experimental
- prospective
What are the different types of randomised controlled trials?
Cluster randomised trials - participants randomised in groups (e.g. by GP centre or therapist) rather than at the individual level
Crossover trials - participants receive both interventions in a randomised order
Multi-arm and factorial trials - two or more interventions evaluated in a single study
Adaptive design trials - accruing information is used to inform planned design adaptations
What are pros of randomised controlled trials?
- Gold standard
- Randomisation reduces potential for confounding
- Can reduce bias via control and blinding
- can determine causal effects
What are cons of randomised controlled trials?
- Randomisation can be unfeasible or unethical
- Require expert management and oversight, particularly for high risk interventions
- Expensive
What are cohort studies?
Non-randomised
Observational
Typically prospective
What are pros of cohort studies?
Useful when random allocation not possible
Can work for rare exposures – select participants on the basis of exposure
Can examine multiple outcomes
