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MRCPsych Part B > Bias > Flashcards

Bias Flashcards

1
Q

Types of error

A

Random
Systematic (bias)

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2
Q

Types of systematic error

A

Measurement bias
Selection bias
Analysis Bias

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3
Q

When is a study said to be internally valid?

A

If results are close to the truth

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4
Q

When is a study said to be externally valid?

A

If results are applicable to clinician seeking the evidence

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5
Q

Another name for external validity?

A

Generalisability

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6
Q

What can compromise the validity of a study

A

Random error
Systematic error
Confounding

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7
Q

What is a random error?

A

Due to chance

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8
Q

Why are all studies subject to random error?

A

They use samples from a population to estimate

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9
Q

What can be used to test probability of random errors?

A

P values
Confidence Intervals

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10
Q

How can random error be reduced?

A

Repeating study elsewhere

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11
Q

What is a systematic error/bias?

A

Error in the way we select patients, measure outcomes or analyse data

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12
Q

What can bias lead to?

A

False conclusions
Over of under-estimation of an effect

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13
Q

At what stage of a study can bias not be controlled for?

A

Analysis stage

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14
Q

How can bias be classified?

A

According to direction of change they produce in study outcome

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15
Q

What is negative bias?

A

Yields estimates closer to null value i.e. no difference between two groups

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16
Q

What is positive bias?

A

Higher magnitude of estimates than the true ones

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17
Q

What is switch-over bias?

A

Change of direction of association

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18
Q

When can switch-over bias occur?

A

Exaggeration of negative or positive bias

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19
Q

When does selection bias occur?

A

When selected groups differ in important factors other than study variables
Uneven diagnostic procedures

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20
Q

What reduces selection bias?

A

Adequate randomisation

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21
Q

Types of selection bias

A

Berkson bias
Neyman bias
response bias
Unmasking bias
Lead-time bias
Referral bias
Diagnostic purity bias
Membership bias

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22
Q

Another name for Berkson bias?

A

Admission rate bias

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23
Q

What is Berkson bias?

A

Difference in rates of admission of cases and controls due to influence of exposure

24
Q

What is another name for Neyman bias?

A

Incidence-prevalence bias

25
Q

What is Neyman bias?

A

When ascertaining causation, one must look for an association between risk factor and incidence, not prevalence.

26
Q

When does response bias occur?

A

When person who responds to invitation to participate in a study differs from those who do not.

27
Q

When is response bias particularly relevant?

A

When evaluating screening tests

28
Q

What is unmasking bias?

A

When risk factor unmasks an event which it is suspected to cause

29
Q

What is lead-time?

A

Difference in time between date of dx with screening and date of sx without screening

30
Q

What cannot be done if lead time is not accounted for?

A

Survival time cannot be compared to unscreened control group of patients

31
Q

What can lead-time bias lead to i.e. if lead time is not taken into account?

A

Increase survival time due solely to advanced date of diagnosis will result in lead time bias

32
Q

What is referral bias?

A

Variation in concentration of exposures or diseases between patients in primary and secondary care

33
Q

What is diagnostic purity bias?

A

Exclusion of comorbidities resulting in a non-representative sample

34
Q

When is diagnostic purity bias a problem?

A

RCTs

35
Q

What is membership bias?

A

Case identification using members of patients organisations leading to systematic differences from non-representatives

36
Q

When do measurement biases occur?

A

When data is not collected in a uniform fashion

37
Q

How can measurement bias be reduced?

A

Blinding

38
Q

Types of measurement bias

A

Recall bias
Reporting bias
Observer bias
Surveillance bias
Work up/verification bias
Misclassification bias
Desirability bias
Hawthorne effect

39
Q

What is recall bias?

A

Subjects often recall risk factors differently depending on their disease status

40
Q

Which studies are vulnerable to recall bias?

A

Case-control studies

41
Q

What is reporting bias?

A

When a larger percentage of case or control subjects are reluctant to report exposure due to attitudes/perceptions/other concerns

42
Q

What is observer bias?

A

When a researcher knowingly or unknowingly evaluates a variable depending on the status of the individual

43
Q

What is surveillance bias?

A

Diseases may be better ascertained in monitored population than in general population

44
Q

What is verification bias?

A

During assessment of validity of a diagnostic test, execution of gold standard test may be influenced by results of new instrument

45
Q

What is misclassification bias?

A

Cases may be misclassified as controls or exposed group may be misclassified as control.

46
Q

When does misclassification bias only occur?

A

If the misclassification is one sided

47
Q

What is non-differential misclassification?

A

Both sides affected equally

48
Q

What can lead to non-differential misclassification?

A

Errors in measurement instruments

49
Q

What can non-differential misclassification lead to?

A

Reduction in observed magnitude of association

50
Q

What is desirability bias?

A

Patients may choose socially desirable answers during data collection, distorting the picture

51
Q

Which type of study is Hawthorne effect prevalent?

A

Cross-sectional surveys using questionnaires

52
Q

Types of analysis bias

A

Contamination
Attrition

53
Q

What is contamination bias?

A

When participants change group

54
Q

What is attrition bias?

A

Patients lost to follow-up

55
Q

What can minimise analysis bias?

A

Intention to treat analysis

MRCPsych Part B (64 decks)

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