Bias

Question 1

Types of error

Answer 1

Random
Systematic (bias)

Question 2

Types of systematic error

Answer 2

Measurement bias
Selection bias
Analysis Bias

Question 3

When is a study said to be internally valid?

Answer 3

If results are close to the truth

Question 4

When is a study said to be externally valid?

Answer 4

If results are applicable to clinician seeking the evidence

Question 5

Another name for external validity?

Answer 5

Generalisability

Question 6

What can compromise the validity of a study

Answer 6

Random error
Systematic error
Confounding

Question 7

What is a random error?

Answer 7

Due to chance

Question 8

Why are all studies subject to random error?

Answer 8

They use samples from a population to estimate

Question 9

What can be used to test probability of random errors?

Answer 9

P values

Confidence Intervals

Question 10

How can random error be reduced?

Answer 10

Repeating study elsewhere

Question 11

What is a systematic error/bias?

Answer 11

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

Question 12

What can bias lead to?

Answer 12

False conclusions

Over of under-estimation of an effect

Question 13

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

Answer 13

Analysis stage

Question 14

How can bias be classified?

Answer 14

According to direction of change they produce in study outcome

Question 15

What is negative bias?

Answer 15

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

Question 16

What is positive bias?

Answer 16

Higher magnitude of estimates than the true ones

Question 17

What is switch-over bias?

Answer 17

Change of direction of association

Question 18

When can switch-over bias occur?

Answer 18

Exaggeration of negative or positive bias

Question 19

When does selection bias occur?

Answer 19

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

Question 20

What reduces selection bias?

Answer 20

Adequate randomisation

Question 21

Types of selection bias

Answer 21

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

Question 22

Another name for Berkson bias?

Answer 22

Admission rate bias

Question 23

What is Berkson bias?

Answer 23

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

Question 24

What is another name for Neyman bias?

Answer 24

Incidence-prevalence bias

Question 25

What is Neyman bias?

Answer 25

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

Question 26

When does response bias occur?

Answer 26

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

Question 27

When is response bias particularly relevant?

Answer 27

When evaluating screening tests

Question 28

What is unmasking bias?

Answer 28

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

Question 29

What is lead-time?

Answer 29

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

Question 30

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

Answer 30

Survival time cannot be compared to unscreened control group of patients

Question 31

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

Answer 31

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

Question 32

What is referral bias?

Answer 32

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

Question 33

What is diagnostic purity bias?

Answer 33

Exclusion of comorbidities resulting in a non-representative sample

Question 34

When is diagnostic purity bias a problem?

Answer 34

RCTs

Question 35

What is membership bias?

Answer 35

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

Question 36

When do measurement biases occur?

Answer 36

When data is not collected in a uniform fashion

Question 37

How can measurement bias be reduced?

Answer 37

Blinding

Question 38

Types of measurement bias

Answer 38

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

Question 39

What is recall bias?

Answer 39

Subjects often recall risk factors differently depending on their disease status

Question 40

Which studies are vulnerable to recall bias?

Answer 40

Case-control studies

Question 41

What is reporting bias?

Answer 41

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

Question 42

What is observer bias?

Answer 42

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

Question 43

What is surveillance bias?

Answer 43

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

Question 44

What is verification bias?

Answer 44

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

Question 45

What is misclassification bias?

Answer 45

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

Question 46

When does misclassification bias only occur?

Answer 46

If the misclassification is one sided

Question 47

What is non-differential misclassification?

Answer 47

Both sides affected equally

Question 48

What can lead to non-differential misclassification?

Answer 48

Errors in measurement instruments

Question 49

What can non-differential misclassification lead to?

Answer 49

Reduction in observed magnitude of association

Question 50

What is desirability bias?

Answer 50

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

Question 51

Which type of study is Hawthorne effect prevalent?

Answer 51

Cross-sectional surveys using questionnaires

Question 52

Types of analysis bias

Answer 52

Contamination | Attrition

Question 53

What is contamination bias?

Answer 53

When participants change group

Question 54

What is attrition bias?

Answer 54

Patients lost to follow-up

Question 55

What can minimise analysis bias?

Answer 55

Intention to treat analysis