Type of Bias

Question 1

Spectrum bias

Answer 1

Purposefully excluding ‘difficult to diagnose’ patients

Question 2

What is the effect of spectrum bias?

Answer 2

The index test appears more successful at diagnosing

Question 3

Review bias

Answer 3

If interpretation of the index test is not independent and blind to the reference standard

Question 4

What is the effect of review bias?

Answer 4

The index test appears more accurate

Question 5

Verification bias

Answer 5

Tendency not to give the reference standard test to patients who were negative on the index test, because the reference standard is more invasive

Question 6

What is the effect of verification bias?

Answer 6

Over/underestimation of the index test accuracy

Question 7

Selection bias

Answer 7

Systematic differences in the selection process of exposure groups

Question 8

What is the effect of selection bias?

Answer 8

Groups cannot be validly compared with each other, or the general population

Question 9

What are two types of selection bias?

Answer 9

Sampling bias
Response bias

Question 10

Sampling bias

Answer 10

Certain individuals/groups are systematically more likely to be chosen than others

Question 11

Response bias

Answer 11

Systematic differences in the characteristics of non-responders vs responders

Question 12

What is the effect of response bias?

Answer 12

The participants may be representative the type of people who are more likely to respond to a survey, who may share other systematic differences to non-responders, therefore the chosen population is not representative

Question 13

Information bias

Answer 13

Systematic differences in the method of obtaining data

Question 14

What are five types of information bias?

Answer 14

Recall bias
Recording bias
Interviewer bias
Lost-to-follow-up bias
Social acceptability bias

Question 15

Recall bias

Answer 15

Patients with the disease think more about health than healthy patients, therefore have more accurate knowledge/memory of exposure

Question 16

Recording bias

Answer 16

Patients with the disease have more extensive medical notes and information than healthy patients, therefore more informed conclusions can be made from these patients

Question 17

Interviewer bias

Answer 17

The interviewer knows whether the patient has the disease or not, and subconsciously alters their questions or question style

Question 18

Lost-to-follow-up bias

Answer 18

Patients who are lost to follow-up, because of illness, are more likely to have data of interest than control patients

Question 19

Social acceptability bias

Answer 19

Interviewee tries to make responses ‘socially acceptable’, therefore is dishonest

Question 20

Healthy-worker effect

Answer 20

The cohort may exclude some individuals in the general population who are not fit enough to be included in the study, therefore this demographic is not represented

Question 21

Performance bias (control group)

Answer 21

The control group receive the intervention anyway, causing contamination, or they seek complimentary treatments, or HCPs give extra treatment

Question 22

Performance bias (intervention group)

Answer 22

More contact with HCPs means that health problems might be detected sooner, and additional healthcare advice might be given than in the control group

Question 23

Detection bias

Answer 23

Systematic differences in how outcomes are determined or how odds ratios are presented, because the analyst is not blinded to the grouping of patients

Question 24

What is the effect of detection bias?

Answer 24

Over/underestimate of effect

Question 25

Attrition bias

Answer 25

Selective dropout of some patients who systematically differ from other patients in the study

Question 26

What might cause attrition bias?

Answer 26

Dropouts representing systematically different groups of people
Outcome of sickness/death
Dissatisfaction with allocation, especially if unblinded