Types of Bias

Question 1

What are the two main types of bias?

Answer 1

1/ Selection Bias: Systematic error arising in the process of identifying individuals or groups to take part in a study

2/ Information Bias: Systematic error in measurement of information on expsoures or outcomes on the study participants

Question 2

What is Sampling Bias?

Which study design is it most likely to occur in?

Answer 2

Occurs in non-random selection of people

2/ Any but particularly: Case-Control & Surveys

Question 3

What is allocation bias?

Which study likely to occur in?

Answer 3

May occur if randomisation to tx/ control in RTC is not random

eg: Pt selected to get new tx based on prognosis

2/ RTC

Question 4

What is responder bias?

Which study likely to occur in?

Answer 4

Occurs when people willing to participate in studies to do with health are systematically different from those who don’t

2/ Survey. ALL types of study

Question 5

What is Attrition bias

When is it most likely to occur?

Answer 5

Subjects who don’t complete f/u investigation may be systematically different to those who do complete f/u

2/ Cohort/ RCT

Question 6

What is Publication bias?

Which study likely to occur in?

Answer 6

Studies with more positive results more likely to be published. Over-representation of positive studies may mean bias towards more positive result

2/ Systematic reviews

Question 7

What is Healthy Worker Effect bias?

Which study likely to occur in?

Answer 7

Study and reference population may not be comparable

2/ Occupational cohort studies

Question 8

What are the types of selection bias?

Answer 8

• Selection
• Allocation
• Responder
• Attrition
• Publication
• Healthy work effect

Question 9

Which types of bias are more likely to affect systematic reviews?

Answer 9

• Publication Bias

Question 10

Which types of bias are more likely to affect RTC?

Answer 10

Attrition

Allocation

Observer

Question 11

What are the types of information bias?

Answer 11

• Recall
• Observer/ Interviwer/ Reporting/ Measurement
• Social Desirability

Question 12

What is Recall bias?

Which study likely to occur in?

Answer 12

Systematic difference in recall about a potential exposure by cases and controls

2/ Case-Control

Question 13

What is social desirability bias?

Which studies is it most likely to occur in?

Answer 13

When subject gives an answer they feel best reflects what the researcher would like to hear

2/ ANY particularly survery/ interview

Question 14

What is observer bias?

Which study likely to occur in?

Answer 14

Can occur if interviewer is aware of status of subject- control or case OR drug tx/ placebo. May steer subject to give correct answer

Data collection clarks may look harder to cases of expsures in cases than controls

2/ Case- Control & RCT