Study Design Flashcards
What is a RCT?
intervention study where subjects are randomly allocated to treatment options
What happens during RCT?
- patients given particular drug/intervention/programme of care they don’t usually receive
- then typically randomised to new vs current/placebo treatment
Why are RCTs accepted as ‘gold standard’ of individual
research studies?
They provide sound evidence about treatment efficacy which is only bettered when several RCTs are pooled in a meta-analysis.
Why is choice of comparison group important?
affects how we interpret evidence from a trial
What is sig of comparison of active agent with inert substance/placebo?
likely to give a more favourable result than comparison with another active agent.
When can RCTs be unethical?
Comparison of an active agent against placebo when an existing active agent is available
What happens when an intervention in RCT is programme of care?
common practice for the comparison group to receive the usual care.
What are the benefits of randomisation in RCTs?
- ensures subjects’ characteristics do not affect which treatment they receive.
- allocation to treatment unbiased - treatment groups balanced by subject characteristics in long run and
differences between groups in trial outcome can be attributed as being caused by treatments alone - provides fair test of efficacy for treatments - not confounded by patient characteristics
- makes blindness possible
What is the usual way to do random allocation in RCTS?
using a computer programme based on random numbers.
What is blinding in RCTs?
treatment allocation is concealed from either the subject or assessor or both
Why is blinding done in RCTs?
avoid conscious or unconscious bias in reported outcomes
What is a double-blind trial?
neither the subject nor the assessor knows which treatment is being given
What is a single-blind trial?
if the treatment allocation is concealed from either the subject or the assessor but not both
Why is blindness sig for subjects and accessors?
- subject who knows they’re receiving a new treatment for pain which they expect to be beneficial may perceive/actually feel less pain than he would if he thought he was receiving the old treatment.
- assessor who knows that a subject is receiving new treatment which he expects to work better than the old one, may tend to round up measurements
- If treatment allocation concealed, both patient + assessor will make unbiased assessments of effects of treatments being tested.
What is a placebo?
- inert treatment which is indistinguishable from the active treatment
- In drug trials, often possible to use placebo drug for control which looks + tastes exactly like active drug
Why is placebo important?
makes it possible for both subject + assessor to be blinded
In which situations is blindness not possible in RCT?
- in trials of technologies e.g. trials comparing different types of ventilators - impossible to blind the
clinician - in trials of surgery versus chemotherapy.
When is statistical analysis of RCTs straightforward?
where there are complete data
What is intention to treat analysis?
- direct comparison of treatment groups with subjects being included in the group to which they were originally allocated
- e.g. patient in group A analysed in group A even if they don’t comply/switch treatment
What is sig of ITT analysis?
- only way in which there can be certainty about the balance of treatment groups with respect to characteristics of subjects.
- therefore provides unbiased comparison of the treatments.
What should happen if patients change treatments during RCT?
- should still be analyzed together with patients in their original, randomly allocated group since change of treatment may be related to the treatment itself.
- If patient’s data are analyzed as if they were in their new treatment group, balance in patient characteristics present after random allocation will be lost.
What is per-protocol analysis?
- patients are analysed according to the treatment they have actually received
- may be useful in addition to ITT analysis if some patients have stopped or changed treatment.
What are observational studies?
- subjects receive no additional intervention beyond what would normally constitute usual care.
- Subjects observed in their natural state (in the real world)
What is a case-control study?
investigates causes of disease, or factors associated with a condition
