Bias

Question 1

Allocation bias: type of bias? Type of study?

Answer 1

Selection bias. Systematic differences in how participants are assigned to treatment / control. RCTs

Question 2

Performance bias: type of bias? Type of study?

Answer 2

Information bias. systematic differences in care received by different groups or in exposure to factors other than the exposure of interest. RCTs

Question 3

Detection bias: type of bias? Type of study?

Answer 3

Information bias. Systematic differences in how outcomes are determined between groups. RCTs

Question 4

Attrition bias: type of bias? Type of study?

Answer 4

Information bias. Systematic bias between groups in withdrawal from study. RCTs

Question 5

What is placebo effect and what kind of study would it be observed in?

Answer 5

Beneficial effect observed in a treatment that isn’t actually effective but the patient perceives it be so. Would be observed in the control arm of an RCT.

Question 6

Responder bias: type of bias? Type of study?

Answer 6

Selection bias. Different groups are more likely to take part in a study. Cohort study, case-control

Question 7

Sampling bias: type of bias? Type of study?

Answer 7

Selection bias. Potential study participants do not have an equal chance of being selected for the study. Cohort study.

Question 8

Follow-up bias: type of bias? Type of study?

Answer 8

Information bias. Differences in the way groups are followed up. >30% loss to follow-up: serious issue. Cohort study.

Question 9

Healthy worker effect: type of bias? Type of study?

Answer 9

Selection bias. Working individuals tend to be healthier than the unemployed population. Cohort study.

Question 10

Recall bias: type of bias? Type of study?

Answer 10

Information bias. Differences in recall between groups. Case control study.

Question 11

Spectrum bias: type of bias? Type of study?

Answer 11

Selection bias. Difficult to diagnose patients are excluded which can over-estimate the effect. DTA study.

Question 12

Verification bias: type of bias? Type of study?

Answer 12

Information bias. Not everyone who receives the index test receives the reference standard. DTA study.

Question 13

Review bias: type of bias? Type of study?

Answer 13

Information bias. Analysis of index test and reference standard not independent of one another. DTA study.

Question 14

What types of bias would you find in cohort studies? (4)

Answer 14

Responder, sampling, follow up, healthy worker

Question 15

What types of bias would you find in RCTs? (4)

Answer 15

Allocation, performance, detection, attrition

Question 16

What types of bias would you find in DTA studies? (3)

Answer 16

Spectrum, verification, reviewer

Question 17

What types of bias would you find in case-control studies? (2)

Answer 17

Recall, responder