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Lecture 21 - randomised controlled trials Flashcards

1
Q

Randomised controlled trials

A

Analytic study
Intervention studies
Experiment, do something observe the effect

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2
Q

Could the parents’ decision to vaccinate their children have influenced the findings of the study?

A

Yes

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3
Q

How do we know if randomisation worked?

A
  • Percentages similar
  • Age in both groups same
  • Gender in both groups same
  • Number of medications a day is same
  • Balanced similar
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4
Q

Random selection

A

Randomly select people from source population to become a sample

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5
Q

Randomisation

A

Already have sample

Randomly assign treatment or control

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6
Q

cross over studies

A

Each person gets both treatments and control

confounding is effectively eliminated

only be done for long-term conditions and treatments that are not curative (the treatment effect needs to wear-off during the washout)

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7
Q

“per protocol” analysis: Confounding could occur

A

Lost benefit of randomisation

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8
Q

If participants (or researchers) know which treatment they are on, they may act differently

A

May affect outcome

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9
Q

Blinding an important way to avoid bias

A

Making treatment unknown to people

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10
Q

Many exposures should not be randomised:

• Known harmful toxins or procedures

A

Unethical to do

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11
Q

Baby cot death

A

No equipoise

Unethical’

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12
Q

how might this introduce bias?

A

In terms of study design
Find in effects vs treatments
Pharmaceuticals can make their drugs seem more appealing

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13
Q

But disadvantages

A

Time and money
It can be difficult to achieve blinding
Equipoise (enough uncertainty)
Generalisability? – does it reflect the real-world?

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14
Q

Hierarchy of evidence

whats at top?

A

RCT

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15
Q

intervention study

A

RCT
non RCT

analytic study

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16
Q

Essential elements of an RCT

A

Participants randomly allocated to groups

There is a comparison (control) group

Testing effect of treatments/interventions

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17
Q

What if they didn’t randomise?
Things that may have
influenced parents

A

cost
community outbreak
polio in family member

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18
Q

What if they didn’t randomise?

Things that may have altered the risk of polio

A

Polio was more common in wealthy

A community outbreak ? Outbreaks often missed areas

Likely to have been exposed already

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19
Q

in RCT What determines exposure?

A

confounding factors

factors that determine the exposure may also affect the outcome

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20
Q

In RCT Why do we randomise?

A

People who decide to take a treatment are often different to those who don’t: confounding
• Age and sex
• Health risks
• Views of the health professionals treating them
• Health beliefs and habits

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21
Q

How do RCTs avoid confounding?

A

Participants are randomly assigned to intervention or control groups

Randomisation will not affect the outcome

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22
Q

If enough people are randomised,

should there be the same proportion of confounders in each group?

A

yes

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23
Q

Randomisation / Random Allocation

A

Both known and unknown
confounders should be balanced

Equal chance for each participant to be in either group (intervention / control)

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24
Q

Randomisation means

A

confounding is an unlikely reason for differences in outcomes between groups

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25
Randomisation is not
Random Selection
26
Variants of randomisation
Cluster | Stratified or Block randomisation
27
may be difficult to randomise individuals so what do you do instead
randomise groups (clusters) of participants Examples: GP practices, hospital wards, schools
28
If you want to be certain that important confounders are eliminated. what do you do instead?
Stratified or Block randomisation Examples: randomise individuals within each age group, sex, or hospital
29
what is Cluster Randomisation?
Entire practices are randomised to treatment or control All participants in each practice get the same intervention GPs don’t have to do different things for different patients.
30
what is Stratified or Block Randomisation?
Participants are randomised to treatment or placebo in blocks (or strata) at each hospital. Differences between hospitals will be balanced between treatment and control groups
31
what are Cross-over studies?
Each person gets both treatments - confounding is effectively eliminated Can only be done for long-term conditions and treatments that are not curative (the treatment effect needs to wear-off during the washout)
32
how do you preserve the benefits of Randomisation?
Concealment of allocation: | Intention-to-treat analysis:
33
in RCT | why do you do Concealment of allocation?
Make sure that people can’t cheat and pick the treatment that they prefer
34
in RCT | why do you do Intention-to-treat analysis?
Once participants have been randomised, you don’t change the groups
35
why is it Important that allocation sequence is concealed and unpredictable of participants in RCT?
people could cheat the system and introduce bias
36
What happens if people withdraw from RCT?
Groups no longer similar “per protocol” analysis: Confounding could occur
37
Protect the benefits of randomisation by
analysing people (treated and placebo) as they were randomised – as we Intended To Treat them – regardless of whether they followed the protocol
38
whats Intention-to-treat analysis?
Analyse participants as randomised Reflects the ‘real-world’: people often don’t take treatments Difficult if data are missing – you can’t analyse data you don’t have
39
whats Per-protocol analysis?
Analyse as treated (not necessarily as randomised) Lose the benefit of randomisation Can be appropriate for efficacy trials (does the drug work if you take it?)
40
Bias occurs when a study is conducted in a way that
leads to systematic errors
41
Potential sources of Bias
Lack of Blinding Loss to follow-up Non-adherence
42
whats lack of blinding
If participants (or researchers) know which treatment they are on, they may act differently
43
whats Loss to follow-up?
If people withdraw because of side effects, we may underestimate the harms of treatment
44
whats Non-adherence?
If people don’t take the treatment, we will not learn about its true benefits and harms
45
whats Blinding?
not knowing what treatment a participant was taking influence: avoids bias A research team member? The participant? The participant’s clinician?
46
if Participant knew (or guessed) that you were taking a placebo • Would you be more or less likely to report a benefit from treatment? • How about side effects?
may act differently | may affect outcome
47
what does “Single blind” mean?
participants
48
what does “Double-blind” mean?
participants and the researchers
49
Who is blinded?
* The participant * The researchers who give the treatment * The researchers who collect the data * The data analyst
50
Blinding Important, but can be challenging to achieve in practice... You can usually get a matching placebo pill But what about surgical or physiotherapy treatment?
Safety and ethical concerns
51
Intention to Treat analyses:
Analyse participants in the groups they were randomised to
52
Loss to follow-up
You don’t know what happened (did they get better or worse?) You can’t analyse data that you don’t have Confounding and Bias may occur
53
Non-adherence
Participants often don’t do what you ask them to:
54
Non-adherence | Participants often don’t do what you ask them to:
* Only take some treatment or stop it altogether * Don’t turn up for appointments * Take alternative treatments (including the intervention or control)
55
If there is too much non-adherence,
difficult to interpret the study
56
Strengths of RCTs
* best study design to test an intervention * Well conducted studies should eliminate confounding and bias * can calculate Incidence, RR, and RD * strongest design for testing cause-and-effect associations
57
Many exposures can not be randomised: such as
* Low birth weight | * Whether you develop a disease
58
Many exposures should not be randomised such as
Known harmful toxins or procedures
59
Many exposures are very difficult to randomise such as
* Long-term behavioural changes | * Common exposures in the community (how do you avoid them?)
60
what does Need to have clinical equipoise mean?
Genuine uncertainty about benefit or harm of intervention
61
what is unethical?
- Give known harmful interventions to people - Give interventions known to be less effective than current treatments - Waste resources and risk harm if we already know the answer
62
how can RCTs be very expensive?
* may need large numbers of participants * ensure complete follow-up * can take a long time
63
RCT Often funded by pharmaceutical companies:
* potential for big profits if the drug works | * unlikely to fund studies of cheap treatments with little chance of profit
64
Participants in RCTs are often not representative:
* They need to meet all the inclusion criteria * AND be willing to participate This can affect generalisability:
65
Like cohort studies, RCTs are not efficient for rare outcomes
Rare adverse drug effects are often not found by RCTs | usually found by post-marketing surveillance
66
Cohort vs. RCT
Cohort - Ascertain exposure status, then follow-up to find out outcome(s) - Observational study Randomised Controlled Trial - Randomly assign exposure, then follow-up to find out outcome(s) - Interventional (experimental) study
67
RCT strengths
random allocation to exposure * Low risk of bias and confounding * Can calculate incidence, relative risks, and risk differences * Best way to test interventions
68
Protecting Randomisation
``` Large numbers Conceal allocation Blinding Complete follow-up Intention-to-Treat ```
69
what do large numbers in RCT do?
Better balance of confounding between groups
70
what do Conceal allocation in RCT do?
Prevents cheating during randomisation process
71
what do Blinding in RCT do?
Reduces chance of bias during the study
72
what do Complete follow-up in RCT do?
Preserves randomisation groups
73
what do Intention-to-Treat in RCT do?
Preserves randomisation groups
74
hierarchy of evidence | from low chance of bias and confounding to high chance of bias and confounding
``` RCT cohort case control cross sectional case study ideas, experts, opinions, editorials anecdotal ```
75
what are some limitations of RCT?
Time and money It can be difficult to achieve blinding Equipoise Generalisability? – does it reflect the real-world?

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