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BMSc Statistics > Section 7 (Pgs 81-86) > Flashcards

Section 7 (Pgs 81-86) Flashcards

1
Q

What is the word used to describe a study where the subjects undergo an intervention?

A

Experimental

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2
Q

What is the word used to describe a study where the subjects are monitored?

A

Observational

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3
Q

What do experimental studies typically do?

A

Compare treatments or assess the outcome of surgery

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4
Q

What do observational studies typically do?

A

Determine risk factors for disease

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5
Q

What type of studies are most epidemiological studies?

A

Observational

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6
Q

What is the disadvantage of observational studies?

A

Usually less powerful than experimental designs because the conditions have not been controlled in any way by the researcher

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7
Q

What is the word used to describe a study where the study is based on a review of existing data e.g. patient records?

A

Retrospective

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8
Q

What is the word used to describe a study is based on data which has to be collected at some time in the future?

A

Prospective

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9
Q

Describe a typical retrospective study? (2)

A

Review of a patients’ lifestyles to identify risk factors for a disease or review of medical records to determine the effect of a previous intervention

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10
Q

Describe a typical prospective study? (2)

A

Trials for comparing treatments, or assessing the input of an intervention on a patient’s condition

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11
Q

What is the word used to describe a study where each subject is observed once providing a snapshot of a situation?

A

Cross-sectional

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12
Q

Give examples of a typical cross-sectional study? (3)

A

Surveys
Investigation of the incidence of a disease in a population
Laboratory experiments

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13
Q

What is the word used to describe a study that monitors a situation over time?

A

Longitudinal

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14
Q

What is the word used to describe a study where the subjects are unaware of which treatment they haven been given?

A

Blind

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15
Q

What is the word used to describe a study in which neither the subjects nor the person monitoring their progress has knowledge of the treatment given?

A

Double blind

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16
Q

Are blind and double blind trials observational or experimental?

A

Experimental

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17
Q

What is the word used to describe a study where the subjects are selected at random?

A

Randomised

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18
Q

What effect does randomisation have on confounding factors?

A

Randomisation balances out confounding factors, both known and unknown

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19
Q

Compared to randomisation, what is a more powerful way of dealing with known confounding factors?

A

To use them to stratify the population and select subjects randomly from each stratum

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20
Q

What is called when known confounding factors are used to stratify the population and select subjects randomly from each stratum?

A

Randomised stratified trial

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21
Q

What is the word used to describe observations when variables are measured more than once on each subject or subjects are matched for factors critical to the outcomes?

A

Dependent

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22
Q

What is the word used to describe observations when variables measured are not related?

A

Independent

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23
Q

Are designs based on independent or dependent data more powerful?
Why?

A

Dependent data

Some of the greatest variation (between subjects) has been removed

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24
Q

What is the word used to describe a study which includes a comparison group of subjects who are not given the treatment?

A

Controlled

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25
Q

What is the word used to describe a study in which the control is a placebo?

A

Placebo-controlled

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26
Q

Describe a parallel group design?

A

one in which the treatment and control groups are observed at the same time

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27
Q

What is the name for a parallel group study in which each individual subject who received the treatment is matched for factors critical to the outcomes with a subject in the control group?

A

Case-controlled

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28
Q

What is the name for a parallel group trial which continues until a difference between the treatment and control groups becomes apparent?

A

Sequential

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29
Q

What is the name for a controlled trial in which each subject acts as their own control?

A

Crossover design

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30
Q

What must be ensured when carrying out a crossover study?

A

Ensure there is no carry-over effect from one treatment to another

31
Q

Why are case-controlled and crossover designs efficient?

A

Because some of the between-subjects variation has been removed

32
Q

What happens in a prospective cohort trial?

A

A group of subjects who are initially disease-free are followed over time (factors subjects are exposed to are recorded over time)

33
Q

What are the disadvantages of prospective cohort studies?

A

They are large and costly and take many years to provide results

34
Q

What kind of disease are prospective cohort studies unsuitable for?

A

Rare diseases

35
Q

What happens in a retrospective cohort study?

A

Patients without disease are looked back on to see what risk factors they were exposed to

36
Q

What is a case control study?

A

A retrospective study of diseased subjects looking at range of factors they have been exposed to to establish risk of disease

37
Q

What is the key difference between a case control and a cohort study?

A

A cohort study starts with the risks looking at whether disease develops (retro. = data exists, prospective = follow up subjects) where as a case control study start with patients who have the disease and looks back for risks

38
Q

What is an advantage of case control studies?

A

Cheap

39
Q

What is a disadvantage of a case control study?

A

Subject to bias because subjects are not chosen randomly

40
Q

What is the name for non-randomised studies?

A

Quasi-experimental studies

41
Q

What is the main disadvantage of quasi-experimental studies?

A

Not randomised and therefore susceptible to bias

42
Q

Does a cohort or case control study start with the disease?

A

Case control

43
Q

Does a cohort or a case control study start with the exposure?

A

Cohort

44
Q

What is at the bottom for the pyramid of evidence? (3)

A

Cross-sectional, case reports, expert opinion

45
Q

What is the 2nd level up on the pyramid of evidence?

A

Observational studies such as case-control and cohort studies

46
Q

What is the middle layer in the pyramid of evidence?

A

RCT’s

47
Q

What is the 2nd top level in the pyramid of evidence?

A

Systematic review

48
Q

What is the top level of the pyramid of evidence?

A

Meta-analysis

49
Q

What should you do before starting a study to test its design?

A

A pilot study

50
Q

What are the 3 types of experimental studies?

A

RCT’s
Crossover studies
Quasi-experimental studies

51
Q

What are the 4 types of observational studies?

A

Case-control
Cohort (retrospective and prospective)
Cross-sectional

52
Q

What is the main advantage of a crossover trial over a parallel group design?

A

The principal source of variation between subjects is removed entirely as each subject is their own control - therefore if there are real treatment effects, a crossover trial is more able to detect them than a parallel group study

53
Q

Are crossover trials or parallel group trails more powerful?

A

Crossover trials (therefore fewer subjects are needed for these)

54
Q

Does trial designs in which between subject variation is removed more or less powerful?
What does this mean

A

More powerful

Require fewer subjects

55
Q

What is the principle weakness of the crossover trial?

A

Danger of one treatment having a carry-over effect

56
Q

How can the risk of having a carry-over effect in crossover trials be removed? (2)

A

By having a period between successive treatments (a wash out period) which is sufficiently long for the first treatment to be fully out of a subject’s system
Randomising the order of the allocation of the treatments

57
Q

Give a circumstance when a parallel group trial would be more appropriate than a crossover study?

A

When participants can only be exposed to one treatment e.g. in a study to compare the impact of 2 training programmes on performance

58
Q

Give the 3 main disadvantages of cohort studies?

A

They are large, costly and take a long time to produce results, particularly if the disease under consideration is rare

59
Q

Give the main advantage of cohort studies?

A

the subjects are randomly chosen and therefore free from bias

60
Q

What are the 2 main advantages of case control studies?

A

Cheap

Provide speedy results

61
Q

What is the main disadvantage of case control studies?

A

Subjects are not randomly chosen (any trial that is not randomised is vulnerable to bias and therefore the conclusions that can be drawn are limited)

62
Q

What is the main indication for a cohort study over a case control study?

A

Occurrence being investigated is common

63
Q

What is the main indication for a case control study over a cohort study?

A

Investigation of the risk factors for a rare disease

64
Q

What are the 6 factors that determine what sample size will be sufficient to detect a real treatment effect?

A 
Significance level of the test
Power of the test required 
Size of the effect to be identified
Standard deviation of the measurements
Study design
Practical issues e.g. what is realistically available, for example, financially
65
Q

What is the symbol for significance level?

A

Alpha

66
Q

What is the symbol for power of the test?

A

Beta

67
Q

What is the significance level usually set at?

A

5%

68
Q

What is the power of the test almost always set at?

A

80%

69
Q

What happens to sample size required as the variation in a measure increases?

A

Sample size also increases

70
Q

What is the easiest way to estimate the standard deviation of the measurements involved in a study?
What if this information is not available?

A

To review the results from previous similar investigations

Need to carry out a small pilot study

71
Q

What feature about study design will affect sample size?

A

How much between-subject variation is removed e.g. it is removed totally in a crossover and partially in a case-control = fewer subjects required

72
Q

Equation for sample size in a two group parallel trial, with sig. level 5% and power 20%?

A

n = 16s squared/ d squared

73
Q

What happens to sample size needed as the size of the effect to be identified decreases?

A

Decreases

BMSc Statistics (9 decks)

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