Jackson: Anatomy of a RCT Flashcards
Why do a RCT?
- Gold standard for ‘if a treatment/intervention work’
- Reduces confounding biases
- Triangle: people in study
- Circle: exposed and the other side a control
- Outcomes over time
put this into the GATE framework
- Triangle (participants): clean elective operations, stratified by risk
- Circle:
- exposed group: IV cefotaxime
- Control group: identical placebo
- Time: 4-6 wks
- Outcomes: Surgical site infection
Tria was ‘double blind’ and randomised
How did they do randomisation of this trial? Why?
Low and high-risk patients were randomly assigned separately by the pharmacist in blocks of four to receive IV Cefotaxime (2gm) or an identically labeled placebo. The AB was mixed in 100ml 5% dextrose in water and was infused rapidly on call for operation. No other ABs were permitted.
When you randomised, by chance you should get ~50% of high and low risk. BUT in small groups, this doesn’t always occur, which is why you should stratify first into risk to avoid confounding by this.
Block randomisation: makes sure you get the same amount in the intervention then the comparison (take ‘blocks’ of 4,6,8 people).
Blinding: patient doesn’t know
Double blinding: both patient and those doing treatment/follow up don’t know.
Describe the concept of allocation concealment and double blinding
So that the way people are getting into a control or an intervention group is not controlled/influenced at any point by anyone looking after the patient.
Lots of new drug trials used to have patients put into a trial and not randomise it order to ensure their patient got the new treatment. This stuffed up the process of randomisation. NOW we conceal it also from the doctor, and go through an uninvolved 3rd party.
“concealed allocation or double blind”
What is concealed allocation?
Concealed allocation is a procedure implemented in a randomized control trial where the individuals screening and separating the candidates into two (or more) arms of a study are blinded. This is a consideration beyond blinding the practitioner delivering the care or the patients receiving the care.
What can you see from the baseline characteristics of this RCT?
That the two groups (intervention and placebo) have relatively similar characteristics. From this, we can conclude they were effectively randomised.
What are the numbers of this study in a GATE framework.
What is EGO and CGO?
- EGO: a/EG
- a= risk of outcome in the exposed group
- EG: Exposed Group
- CGO: b/CG
- b= risk of outcome in comparison group
- CG= comparison group
Although the ‘intention to treat’ group of participants was 316 and 317 (t = 633) the actual ‘on-treatment’ numbers were 312 and 313 as EG lost 3 and CG lost 5. Therefore this was not a massive deal.
EG lost 5 to follow up (f/u) and CG lost 4 to f/u. These are removed from the on-treatment numbers → 308 and 309. This isn’t always done, but it doesn’t matter what number you use in the denominator (on-treatment, f/u or intention to treat) as long as they’re all the same!! But COULD be a big deal to the numerators
Often if the loss to f/u is <20% its not a big deal
What happens if instead of one rug/placebo right before surgery, the RCT is a drug that needs to be taken daily? How would you modify you RCT?
Often you have a much smaller ‘on-treatment’ group then an ‘intention-to-treat’ group as people have lower compliance/complications.
The Treatment group
What are the strengths and weaknesses of RCTs?
weaknesses:
- ethics
- compliance
- non-real world conditions
- expensive - leading to being small = inc random error
- publication bias
Strengths
- gold-standard
- Allows you to establish causation
- low confounding
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EGO, CGO, RR and RD?
EGO = Exposure group / outcomes
CGO = Control group / outcomes
Relative risk = EGO/CGO
Risk difference = EGO - CGO
Questions to ask when deciding if to treat based off RCT?
If I don’t treat this patient what is their probability of having a negative event?
How does this RR translate into absolute risk in THIS patient?
