Clinical Trials to Treat Heart Disease Flashcards
What is an intervention study?
Intervention study→ experiment where there is an intervention to evaluate its efficiency and safety.
Participants sorted into untreated, standard therapy or placebo group. Aka experimental, clinical trial or RCT.
The key design features of clinical trial are random allocation, control group, blinding. Describe random allocation
- Randomisation = individuals allocated randomly to each treatment/control group
- Avoids allocation bias- both groups have similar features
- Differences in health outcomes between intervention and control groups is attributed to intervention - not characteristics
- Randomisation is not the same as random sample of people
The key design features of clinical trial are random allocation, control group, blinding. Describe control group
needed as some patients will get better on their own
- Placebo effect e.g. sugar pill.
- Based on person’s own self-healing capacity – triggered by belief that they’re receiving medication
- sometimes receive no active treatment (placebo only)
- sometimes receiving usual care i.e normal pattern of treatment w/o new intervention
What is the difference between double blind and single blind?
Double blind → neither patient nor observer know which group patient is allocated to.
Single blind → either patient or observer don’t know which group patient allocated to
The key design features of clinical trial are random allocation, control group, blinding. Describe blinding
Blinding of observers/assessors avoids:
Selection bias (who to invite to trial)
Assessor bias (how outcome is recorded)
Keeps assessors objective (decisions to withdraw patients/amount of encouragement)
Blinding of participants avoids:
Selection bias (whether to participate in trial)
Response/recall bias (differences in how outcomes reported by participants)
Participant non compliance
Describe the cross over design trials
- all participants receive the same 2 or more treatments, but the order in which they receive them depends on the group which they are randomly assigned to
What are the adv and disadv of cross over trials?
Advantage: Need fewer participants (they act as their own controls and within-individual comparisons are made, rather than between-individual comparisons)
Disadvantages:
–cannot be used to assess treatments with prolonged effects (which may carry over into the second period)
–Disease may not remain stable over trial period
–More burden on participants, longer trial period, maybe more drop-outs
Describe parallel design trials
If the randomized controlled trial has been well-conducted, a difference in outcome between intervention and control groups will reflect either:-
a causal relationship OR chance/random error
BUT NOT due to bias or confounding
What is intention to treat?
Carries out the analysis on the basis of original randomization, so ignores crossovers/ dropouts and thus avoiding bias
Is likely to underestimate effect of intervention (depending on how much `crossover’ took place)
BUT – this provides an UNBIASED estimate of intervention effect
Should be main analysis presented in most situation
What is trial analysis per protocol?
- Per protocol analysis
- Carries out the analysis on the basis of the treatment actually taken
- Less likely to underestimate effect of intervention
- BUT may be BIASED (depends on dop out number + characteristics)
- Should generally be a subsidiary analysis
25 in every 278 people die using propanolol
37 in 282 people die using the placebo.
Use this information to define risk and relative risk
Risk = risk of developing disease over time in one group
Relative risk = comparison of 2 groups’ risk (or ratio)
Eg: Risk of death in propranolol = 25/278 = 0.09. Risk of death in placebo = 37/282 = 0.13
Relative risk = 0.09/0.13 = 0.69
Risk of death in propranolol is 0.69 times risk in placebo
What is NNT and ARR?
Use these values: risk of propanolol and control= 0.13 and 0.09
Number needed to treat (NNT) – how many patients need to treat to prevent additional outcome:
Risk difference of propranolol and control = 0.13-0.09 = 0.04 (4%) (absolute risk reduction – ARR)
If 100 people treated using propranolol, 4 less people die NNT = 25 (1/0.04)
NNT is inverse of ARR
