Bias & Misclassification

Question 1

What three aspects must researchers evaluate of their study (internal validity) before declaring a real and true association?

Answer 1

1. Check for Confounding or Effect Modification
2. Check for Bias
3. Check for Statistical Significance

Question 2

What is the definition of bias?

Answer 2

Systematic (non-random) error in study design of conduct leading to erroneous results

Question 3

What does bias distort?

Answer 3

The relationship between exposure and outcome

Question 4

What are the elements which bias has potential to impact?

Answer 4

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

Question 5

Is bias capable of accounting entirely for a weak association (RR/OR)? How about a very strong association?

Answer 5

• Yes

- No

Question 6

Can bias over- or under-estimate the true measure of association?

Answer 6

Yes

Question 7

Can bias have an enhancing or minimizing effect not eh true measure of association?

Answer 7

Yes

Question 8

What are the two main categories of bias?

Answer 8

1. Selection-related

2. Measurement-related

Question 9

Define selection-related.

Answer 9

Any aspect in the way the researcher selects or acquires study subjects which creates a systematic difference between groups

Question 10

Define measurement-realted.

Answer 10

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

Question 11

What is measurement-related also known as?

Answer 11

Information/observation

Question 12

What are the types of selection bias?

Answer 12

1. Healthy-worker bias

2. Self-selection/participant (responder) bias

Question 13

What is significant about the self-selection/participant (responder) bias?

Answer 13

Those wishing to participate may be different in some way to those that don’t volunteer/self-select to participate

Question 14

What are the measurement subject-related biases?

Answer 14

1. Recall
2. Hawthorne effect
3. Contamination
4. Compliance/Adherence
5. Lost to follow-up

Question 15

What is Recall bias?

Answer 15

A different level of accuracy/detail in provided information between study groups

Question 16

What is the Hawthorne Effect?

Answer 16

Individuals alter/modify their behavior because they are part of a study and know they are under observation

Question 17

What is Contamination?

Answer 17

Members of the control group accidentally, or outside of the study protocol, receive the treatment or are exposed to the intervention being studied

Question 18

What is Compliance/Adherence?

Answer 18

Groups being interventional studied have different compliance/adherence with study protocol/treatments

Question 19

What is Lost to Follow-Up?

Answer 19

Groups being studied have different withdrawal or lost to follow-up rates or there are other differences between those that stay in the study and those that withdraw or are lost to follow up

Question 20

Under what bias does differential vs. non-differential fall?

Answer 20

Lost to Follow-up

Question 21

What are the observer-related biases?

Answer 21

1. Interviewer

2. Diagnosis/Surveillance (Expectation)

Question 22

What is the Interviewer bias?

Answer 22

The interviewer’s knowledge may influence structure and tone of the interview, which may in turn influence the response from the study subject

Interventions/treatments may not be applied equally between groups, can be conscious or unconscious actions of the interviewer

Question 23

What is the Diagnosis/Surveillance (Expectation) bias?

Answer 23

• 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 – a “Hawthorne-like” effect from the researchers’ perspective

Question 24

What is the Screening-related bias?

Answer 24

Lead-Time

Question 25

What is Lead-Time bias?

Answer 25

An apparent benefit from a healthcare screening due to the early detection of disease despite an unchanged clinical outcome

Question 26

What is Misclassification Bias?

Answer 26

Error in classifying either disease or exposure status, or both

*Source of measurement (information/observation) bias

Question 27

What is non-differential?

Answer 27

• Error in both groups, equally
• Misclassification of exposure or disease which is unrelated to the other (disease or exposure) depending on study design

Question 28

What is the effect of non-differential?

Answer 28

For dichotomous variables, can move the measure of association (RR/OR) towards 1.0; it attenuates you effect estimates of association

Question 29

What is differential?

Answer 29

• Error in one group differently than other

- Misclassification of exposure or disease is related to the other (disease or exposure) depending on study design

Question 30

What is the effect of differential?

Answer 30

Bias can move the measure of association (RR/OR) in either direction in relation to 1.0; it can inflate or attenuate your effect estimates of association

Question 31

How do you control for biases?

Answer 31

1. Blinding/masking
2. Use multiple sources to gather all information
3. Randomly allocate observers/interviewers for data collection
4. Build in as many methods necessary to minimize loss to follow-up