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Pop health > Lecture 21 - randomised controlled trials > Flashcards

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
Q

Randomisation is not

A

Random Selection

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26
Q

Variants of randomisation

A

Cluster

Stratified or Block randomisation

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27
Q

may be difficult to randomise individuals so what do you do instead

A

randomise groups (clusters) of participants

Examples: GP practices, hospital wards, schools

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28
Q

If you want to be certain that important confounders are eliminated. what do you do instead?

A

Stratified or Block randomisation

Examples: randomise individuals within each age group, sex, or hospital

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29
Q

what is Cluster Randomisation?

A

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.

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30
Q

what is Stratified or Block Randomisation?

A

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

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31
Q

what are Cross-over studies?

A

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
Q

how do you preserve the benefits of Randomisation?

A

Concealment of allocation:

Intention-to-treat analysis:

33
Q

in RCT

why do you do Concealment of allocation?

A

Make sure that people can’t cheat and pick the treatment that they prefer

34
Q

in RCT

why do you do Intention-to-treat analysis?

A

Once participants have been randomised, you don’t change the groups

35
Q

why is it Important that allocation sequence is concealed and unpredictable of participants in RCT?

A

people could cheat the system and introduce bias

36
Q

What happens if people withdraw from RCT?

A

Groups no longer similar

“per protocol” analysis: Confounding could occur

37
Q

Protect the benefits of randomisation by

A

analysing people (treated and placebo) as they were randomised – as we Intended To Treat them – regardless of whether they followed the protocol

38
Q

whats Intention-to-treat analysis?

A

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
Q

whats Per-protocol analysis?

A

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
Q

Bias occurs when a study is conducted in a way that

A

leads to systematic errors

41
Q

Potential sources of Bias

A

Lack of Blinding
Loss to follow-up
Non-adherence

42
Q

whats lack of blinding

A

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

43
Q

whats Loss to follow-up?

A

If people withdraw because of side effects, we may underestimate the harms of treatment

44
Q

whats Non-adherence?

A

If people don’t take the treatment, we will not learn about its true benefits and harms

45
Q

whats Blinding?

A

not knowing what treatment a participant was taking influence:

avoids bias

A research team member?
The participant?
The participant’s clinician?

46
Q

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?

A

may act differently

may affect outcome

47
Q

what does “Single blind” mean?

A

participants

48
Q

what does “Double-blind” mean?

A

participants and the researchers

49
Q

Who is blinded?

A
  • The participant
  • The researchers who give the treatment
  • The researchers who collect the data
  • The data analyst
50
Q

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?

A

Safety and ethical concerns

51
Q

Intention to Treat analyses:

A

Analyse participants in the groups they were randomised to

52
Q

Loss to follow-up

A

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
Q

Non-adherence

A

Participants often don’t do what you ask them to:

54
Q

Non-adherence

Participants often don’t do what you ask them to:

A
  • Only take some treatment or stop it altogether
  • Don’t turn up for appointments
  • Take alternative treatments (including the intervention or control)
55
Q

If there is too much non-adherence,

A

difficult to interpret the study

56
Q

Strengths of RCTs

A
  • 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
Q

Many exposures can not be randomised: such as

A
  • Low birth weight

* Whether you develop a disease

58
Q

Many exposures should not be randomised such as

A

Known harmful toxins or procedures

59
Q

Many exposures are very difficult to randomise such as

A
  • Long-term behavioural changes

* Common exposures in the community (how do you avoid them?)

60
Q

what does Need to have clinical equipoise mean?

A

Genuine uncertainty about benefit or harm of intervention

61
Q

what is unethical?

A
  • 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
Q

how can RCTs be very expensive?

A
  • may need large numbers of participants
  • ensure complete follow-up
  • can take a long time
63
Q

RCT Often funded by pharmaceutical companies:

A
  • potential for big profits if the drug works

* unlikely to fund studies of cheap treatments with little chance of profit

64
Q

Participants in RCTs are often not representative:

A
  • They need to meet all the inclusion criteria
  • AND be willing to participate

This can affect generalisability:

65
Q

Like cohort studies, RCTs are not efficient for rare outcomes

A

Rare adverse drug effects are often not found by RCTs

usually found by post-marketing surveillance

66
Q

Cohort vs. RCT

A

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
Q

RCT strengths

A

random allocation to exposure

  • Low risk of bias and confounding
  • Can calculate incidence, relative risks, and risk differences
  • Best way to test interventions
68
Q

Protecting Randomisation

A 
Large numbers
Conceal allocation
Blinding
Complete follow-up
Intention-to-Treat
69
Q

what do large numbers in RCT do?

A

Better balance of confounding between groups

70
Q

what do Conceal allocation in RCT do?

A

Prevents cheating during randomisation process

71
Q

what do Blinding in RCT do?

A

Reduces chance of bias during the study

72
Q

what do Complete follow-up in RCT do?

A

Preserves randomisation groups

73
Q

what do Intention-to-Treat in RCT do?

A

Preserves randomisation groups

74
Q

hierarchy of evidence

from low chance of bias and confounding to high chance of bias and confounding

A 
RCT
cohort
case control
cross sectional
case study
ideas, experts, opinions, editorials
anecdotal
75
Q

what are some limitations of RCT?

A

Time and money

It can be difficult to achieve blinding

Equipoise

Generalisability? – does it reflect the real-world?

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