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EAB > Study Design > Flashcards

Study Design Flashcards

1
Q

What is a RCT?

A

intervention study where subjects are randomly allocated to treatment options

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2
Q

What happens during RCT?

A
  • patients given particular drug/intervention/programme of care they don’t usually receive
  • then typically randomised to new vs current/placebo treatment
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3
Q

Why are RCTs accepted as ‘gold standard’ of individual

research studies?

A

They provide sound evidence about treatment efficacy which is only bettered when several RCTs are pooled in a meta-analysis.

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4
Q

Why is choice of comparison group important?

A

affects how we interpret evidence from a trial

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5
Q

What is sig of comparison of active agent with inert substance/placebo?

A

likely to give a more favourable result than comparison with another active agent.

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6
Q

When can RCTs be unethical?

A

Comparison of an active agent against placebo when an existing active agent is available

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7
Q

What happens when an intervention in RCT is programme of care?

A

common practice for the comparison group to receive the usual care.

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8
Q

What are the benefits of randomisation in RCTs?

A
  • 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
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9
Q

What is the usual way to do random allocation in RCTS?

A

using a computer programme based on random numbers.

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10
Q

What is blinding in RCTs?

A

treatment allocation is concealed from either the subject or assessor or both

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11
Q

Why is blinding done in RCTs?

A

avoid conscious or unconscious bias in reported outcomes

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12
Q

What is a double-blind trial?

A

neither the subject nor the assessor knows which treatment is being given

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13
Q

What is a single-blind trial?

A

if the treatment allocation is concealed from either the subject or the assessor but not both

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14
Q

Why is blindness sig for subjects and accessors?

A
  • 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.
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15
Q

What is a placebo?

A
  • 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
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16
Q

Why is placebo important?

A

makes it possible for both subject + assessor to be blinded

17
Q

In which situations is blindness not possible in RCT?

A
  • in trials of technologies e.g. trials comparing different types of ventilators - impossible to blind the
    clinician
  • in trials of surgery versus chemotherapy.
18
Q

When is statistical analysis of RCTs straightforward?

A

where there are complete data

19
Q

What is intention to treat analysis?

A
  • 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
20
Q

What is sig of ITT analysis?

A
  • 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.
21
Q

What should happen if patients change treatments during RCT?

A
  • 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.
22
Q

What is per-protocol analysis?

A
  • 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.
23
Q

What are observational studies?

A
  • subjects receive no additional intervention beyond what would normally constitute usual care.
  • Subjects observed in their natural state (in the real world)
24
Q

What is a case-control study?

A

investigates causes of disease, or factors associated with a condition

25
Q

Who are ‘cases’ in case-control studies?

A

patients with disease/cond of interest selected for inclusion,

26
Q

Who are ‘controls’ in case-control studies?

A
  • A comparison group without the disease is then selected

- cases and controls are compared to identify possible risk/causal factors

27
Q

What is different about case-control studies?

A

usually retrospective in that the data relating to risk factors are collected after the disease has been identified.

28
Q

What are the limitations of case-control studies?

A
  • choice of control group affects comparisons between cases + controls e.g. may choose patients with another cond/healthy patients
  • Exposure to risk factor data usually collected retrospectively either reported by patients/from records and may be incomplete, inaccurate/biased (people with cond have more acute recollection of past events compared to those without)
29
Q

What are benefits of case-control studies?

A
  • quick

- expensive

30
Q

What is a cohort study?

A

observational study that aims to investigate causes of disease/factors related to condition but is longitudinal and starts with unselected group of individuals who are followed up for set period of time

31
Q

When are cohort studies sometimes used?

A

confirm the findings of case-control studies

32
Q

How are cohort studies set up?

A
  • starts with unselected group of ‘healthy’ individuals
  • subjects followed up to monitor the disease/condition of interest + potential risk factors
  • length of follow up chosen to allow sufficient subjects to get the disease + risk factors to be explored
33
Q

What is outcome in the simplest case of cohort study?

A

where there is a single risk factor that is either present or absent, the incidence of disease can be related directly to the presence of the risk factor

34
Q

What is different about cohort studies compared to case-control studies?

A
  • longitudinal - for set time period

- Usually prospective, with the risk factor data being recorded before the disease is confirmed

35
Q

Can cohort studies be retrospective?

A

requires that full risk factor data is obtained on all individuals with and without the disease of interest using data which was recorded prospectively

36
Q

What are the limitations of cohort studies?

A
  • large number subjects needed to obtain enough individuals who get the disease/condition, particularly if it is uncommon
  • length of follow up may be substantial to get enough diseased individuals (needs long follow up) and so cohort study not feasible for rare diseases
  • difficulty in maintaining contact with subjects, particularly if follow-up is lengthy
  • resources required may be v. high - expensive
37
Q

What is benefit of cohort studies?

A

Less biased answer than case-control as data collected prospectively

38
Q

What are cross-sectional studies?

A

sample is chosen and data on each individual is collected at one point in time (may not be exactly the same time point for each subject)

39
Q

When are cross-sectional studies used?

A
  • Surveys of prevalence of disease
  • Surveys of attitudes/views, e.g. studies of patient satisfaction, patient/professional knowledge; studies of behaviour e.g. alcohol use, sexual behaviour etc
  • When inter-relationships between variables are of interest, e.g. study to determine characteristics of heavy drinkers where a cross-sectional study allows comparisons by sex, age etc

EAB (5 decks)

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