Intro to RCTs Flashcards
What are observational studies?
- no intervention
- observe and record behaviour, Sx, attitudes
Association between risk factors and disease/outcomes
Cohort, cross sectional studies
What are experimental studies?
research intervenes deliberately to influence events
records effect of intervention
- effectiveness of new drugs, Rx (comparative)
- RCTs, cross-over trials
What 2 types of outcomes should be considered in a RCT?
- positive: good
- negative: bad
ideally, following I want to increase the abundance of positive ones and reduce negative ones
What kind of study design is RCT?
parallel design: patients randomised to a group, which are studies in parallel
then compare outcomes between Intervention and Control groups
What controls are used in a RCT?
- Standard Rx: active or positive control
- Placebo (negative control)
- No “additional” Rx (unlikely)
these are collectively known as the CONCURRENT CONTROLS: they reflect current natural epidemiology
What is the placebo in the RCT?
referred to as “treatment”
no active therapeutic ingredients
similar appearance and taste as active Rx
- administered in same way
What music new Rx or therapeutic regime RCT include?
a control group: to know how the condition would proceed normally (without new intervention)
allows comparison of how much recovery is down to new drug vs. natural improvement of condition
What is the aim of sampling for any study?
to minimise SELECTION BIAS
e.g. systematic difference between population and sample [characteristics]
What is the purpose of using random allocation to group the participants?
removes ALLOCATION BIAS and minimised confounding
What is the difference between ALLOCATION vs SELECTION bias?
ALLOCATION: bias using characteristics that designate participants to either control or intervention group (certain characteristics for control, certain for intervention)
SELECTION: bias made when choosing the initial sampling population. Results in systematic differences between sample and population and can make the study less representative
How does use of a placebo aid RCT design?
ENSURES BLINDING
- minimises ASSESOR BIAS
- minimises RESPONSE BIAS
(all needed to be able to infer causality)
What is the most ideal situation with sampling a population? Why is this not generally done?
investigate the ENTIRE population
all adults meeting inclusion criteria, potentially infinite
-> v. expensive and time consuming
What are the methods of sampling a population?
- convenience sampling (people taken as they are referred or present)
What is a method of making the sample more representative of the population?
using patients from multiple centres or countries or regions
What the importance of making the sample representative of the general population?
affects ability to GENERALISE study results to rest of population
If this is not possible to do, then there is SELECTION BIAS present
What is a bias?
= systematic difference
(not down to chance, but also may not be deliberate)
e.g. study contains more women or >65yo individuals than general population
this may be influenced by other non-deliberate factors: people who are more likely to volunteer after selection
What is the benefit of random allocation?
probability of an individual being allotted to Rx group is equal
eliminates allocation bias
minimises confounding (there should be no differences in baseline characteristic between groups to explain differences in outcomes
How does random allocation facilitate blinding?
- requires placebo
- double blind
What is the benefit of performing a RCT with double-blinding?
= group allocation blinded to researches and participants
reduces ASCERTAINMENT BIAS: - Response bias (patients)
- Assessment bias (researchers)
What are the advantages of using a placebo?
- RESPONSE BIAS
participants may alter responses if they know which group they are in - may report responses to please researchers
- difference between patient response and “truth”
- ASSESSMENT BIAS
researchers may bias outcomes: subjective interpretation to favour their theory - LOSS TO FOLLOW UP
participants less likely to drop out since they are unaware if they’re in the placebo group or not
What is the ‘TREATMENT RESPONSE’?
the response in the outcome for the intervention group
components: natural epidemiology of condition, placebo effect PLUS treatment effect
What is the ‘PLACEBO RESPONSE’?
response in outcome for the placebo group
components: natural epidemiology of condition PLUS placebo effect
What is the empirical difference between the ‘Treatment’ and ‘Placebo’ responses?
the inclusion of the ‘treatment effect’ in the treatment response
this is the pharmacology (of the intervention)
What is the Hawthorne effect?
It is a non-specific treatment effect;
Change in behaviour as motivational response to interest, care, or attention received through observation and assessment.
