Bias & Misclassification

Question 1

Bias Definition

Answer 1

Systemic (non-random) error in study design or conduct leading to erroneous results.

Distorts the relationship between exposure and outcome

Question 2

3 Components of Bias

Answer 2

1. Source/Type
2. Magnitude/Strength
3. Direction

Question 3

2 Main Categories of Bias

Answer 3

1. Selection Related

2. Measurement Related

Question 4

Selection Related Bias

Answer 4

The way the researcher selects or acquires study subjects that creates a systemic difference between groups

Question 5

Measurement-related Bias

Answer 5

Any aspect in the way the researcher collects information or measures/observes subjects which creates a systemic difference between groups

Question 6

Types of Selection Bias

Answer 6

1. Healthy-Worker Bias

2. Self-Selection/Participant (Responder) Bias

Question 7

Healthy-Worker Bias

Answer 7

Can be seen in prospective Cohort studies

The healthy workers would be taken as part of the study and those who have worked there and died or became sick are not counted. Even though they may have gotten sick because of exposure on the job

Question 8

Self-Selection/ Participant (Responder) Bias

Answer 8

Those that volunteer may be different in some way to those who don’t volunteer

Question 9

3 Main Types of Measurement Bias

Answer 9

1. Subject-Related
2. Observer-Related
3. Screening Related

Question 10

Subject Related Biases

Answer 10

1. Recall (Reporting) Bias
2. Contamination Bias
3. Compliance/Adherence Bias
4. Loss to Follow-up Bias

Question 11

Recall (Reporting) Bias

Answer 11

• differential level of accuracy/detail in provided info between groups
• Those exposed or diseased may have greater recall because they have a greater reason to. They may also exaggerate their responses
• Individuals can report effects differently because they are part of a study

Question 12

Hawthorne Effect

Answer 12

Individuals report differently or change their behavior because they know they are being followed

Question 13

Contamination Bias

Answer 13

Members of control group accidentally receive treatment or are exposed to the intervention being studied.

Question 14

Compliance/Adherence Bias

Answer 14

Groups being interventionally studied have different compliances.

How well do the patients follow the instructions

Question 15

Lost to Follow-up Bias

Answer 15

Groups being studied have different withdrawal rates.

The groups are no longer equal. Either in numbers or personal characteristics

Question 16

Observer-Related Biases

Answer 16

1. Interviewer (Proficiency) Bias

2. Diagnosis/Surveillance (Expectation) Bias

Question 17

Interviewer (Proficiency) Bias

Answer 17

• Systemic difference in soliciting, recording or interpreting on the part of the researcher.
• The knowledge of the interviewer may influence structure, or tone, of questions or follow-up questions which may influence response from study subject
• Interventions/treatments not applied equally between groups due to skill to training differences of study personnel

Question 18

Diagnosis/Surveillance (Expectation) Bias

Answer 18

• Different evaluation, classification, diagnosis or observation between study groups
• Observers may have preconceived expectations of what they should find in examination, evaluation or follow up

Question 19

Screening-Related Bias Example

Answer 19

Lead-Time Bias

Question 20

Lead-Time Bias

Answer 20

An apparent benefit from a healthcare screening due to early detection of disease. Despite unchanged clinical outcome.

Question 21

Misclassification Bias

Answer 21

Error in classifying either disease or exposure status or both

• Non-Differential
• Differential

Question 22

Non-differential

Answer 22

Misclassification of exposure or disease which is Unrelated to the other depending on study design

Effect: bias moves the measure of association closer to 1

Question 23

Differential

Answer 23

Error in one group different than the other.

Misclassification of exposure or disease is related to the other, depending on study design

Effect: Bias can move in all directions

Question 24

Controlling for Bias

Answer 24

• Blinding/Masking
• Use multiple sourced to gather all information
• Randomly allocate observers/interviewers for data collection
• Build in as many methods necessary to minimize loss to follow-up