Lecture 12 - Bias & Misclassification

Question 1

Define bias.

Answer 1

Systematic (non-random) error in study design or conduct that lead to a distortion in the association between exposure and outcome

Question 2

What can be done about be done about bias before a study? After?

Answer 2

Before:
-steps can be taken to avoid bias or minimize its impact

After:
-NOTHING!

Question 3

What are the 3 elements of bias impact?

Answer 3

• Source/Type
• Magnitude/Strength
• Direction

Question 4

What effect can bias have on the magnitude/strength of association?

Answer 4

Bias can entirely account for a weak association but is unlikely to account for a large association.

Question 5

What effect can bias have on the direction of association?

Answer 5

Bias can result in over or underestimation of the measure of association either enhancing or minimizing the true relationship.

Question 6

What are the two main categories of bias?

Answer 6

• selection

- measurement

Question 7

What is selection related bias?

Answer 7

When the way that subjects are selected or acquired creates a systematic difference.

Common in comparative studies when the group are not similar enough or do not adequately represent the population.

Question 8

What is measurement related bias?

Answer 8

When the way that information is collected or the subjects are measured/observed creates a systematic difference.

Question 9

What are examples of selection bias?

Answer 9

• Healthy-worker bias

- Self selection/responder bias

Question 10

What is healthy worker bias?

Answer 10

Type of selection bias in which a group of workers may not be representative because those who are unhealthy due to work may no longer be working.

Commonly seen in prospective cohort studies in which.

Question 11

What is self-selection/responder bias?

Answer 11

Type of selection bias in which those who volunteer to participate in a study might not be representative of the rest of the population.

Question 12

What are the types of measurement bias?

Answer 12

• subject-related
• observer-related
• screening-related

Question 13

What is recall/reporting bias?

Answer 13

Diseased or exposed subjects may be more likely to recall detail OR exaggerate responses

Question 14

What is the Hawthorne effect?

Answer 14

When individuals in a study alter their behavior because they know they are being observed.

Question 15

What is contamination bias?

Answer 15

When individuals in the control group receive treatment outside of protocol similar to intervention being studied.

Question 16

What is compliance/adherence bias?

Answer 16

When groups being studied have different compliance/adherence to study protocol or treatment.

Question 17

What is lost to follow-up bias?

Answer 17

When groups have different withdrawal rates or lost to follow-up rates. Also when there are differences in those who stay and those who withdraw.

Question 18

What is interviewer bias?

Answer 18

When the interviewers knowledge may affect how questions are asked or information is obtained differently between groups.

-also-

When interventions or treatment are administered differently due to differences in skill or compliance of study personel

Question 19

What is diagnosis/surveillance bias?

Answer 19

When the observers preconceived expectations affect the evaluation, classification, diagnosis, or observation differently between groups.

Question 20

What is lead-time bias?

Answer 20

When screening due to the study leads to earlier detection of disease than normal which can lead to the attribution of a greater than actual benefit of the treatment.

Question 21

What is misclassification?

Answer 21

Error in classifying either disease or exposure status

Question 22

What are the types of misclassification?

Answer 22

• non-differential

- differential

Question 23

What is non-differential misclassification?

Answer 23

• misclassificaiton occurs equally in both groups

- attenutate measure of association; moves closer to 1.0

Question 24

What is differential misclassification?

Answer 24

• misclassification occurs more frequently in one group than the other
• inflates or attenuated the measure of association; moves closer OR away from 1.0

Question 25

What are methods for controlling bias?

Answer 25

• blinding/masking
• multiple sources to gather data
• randomly allocate observers/interviewers
• use technology as much as possible
• attempt to minimize loss to follow-up