DL: Bias

Question 1

What is bias?

Answer 1

Any trend in data the can lead to a conclusion that could be untrue

Systematic error in any part of the trial

Question 2

What aspects of a study is susceptible to bias?

Answer 2

1. Selection of subjects
2. Performance of the trial
3. Measurement of the outcome
   4.Data collection
4. Data analysis
   6.Data interpretation
5. Reporting the findings

Question 3

What are the major categories of bias?

Answer 3

Selection and information

Question 4

What is selection bias?

Answer 4

A distortion in the estimate of statistic of interest → method of selecting subjects in the treatment group and control group

Question 5

What are the types of selection bias?

Answer 5

1. Sampling
2. Ascertainment
3. Confirmation
4. Publication
5. Exclusion

Question 6

What is sampling bias?

Answer 6

Some members of the target population are more likely to be selected from the trial over others

Question 7

What is ascertainment bias?

Answer 7

Patients selected for a study are not representative of all classes in a population

Surveillance or detection bias

Question 8

Identify the type of bias:
Emergency medicine study enrolled patients only during day time hours

Answer 8

Sampling bias

Question 9

What is ascertainment bias?

Answer 9

Patients selected for a study are not representative of all classes in the population

Surveillance or detection bias

Question 10

Identify the type of bias:
Obese patients are more likely to undergo medical examinations, blood tests, and imaging studies than non-obese people. If obese subjects were being compared to non-obese subjects for risk of certain cancers, early cancers would be more likely to be found in the obese group, causing an overestimate of the true association.

Answer 10

Ascertainment bias

Question 11

What is confirmation bias?

Answer 11

Tendency to interpret new evidence as confirmation of existing beliefs

Favoring data that confirms existing beliefs

Question 12

Identify the type of bias:
In 2015, former president of the National Lipid Association advocated
for statin use in the elderly. Cited one CT of statin therapy which reported a reduction in cardiovascular disease in the elderly. Ignored the other published CT of statin in elderly which reported no significant reduction.

Answer 12

Confirmation bias

Question 13

What is publication bias?

Answer 13

Occurs when all trials are not published

Question 14

What kind of trials are excluded with publication bias?

Answer 14

Those that fail to show an effect or that show harm

Question 15

Interpret the funnel graph

Answer 15

Question 16

What does a bias funnel graph look like?

Answer 16

Question 17

What is exclusion bias?

Answer 17

Investigators apply different eligibility criteria to different groups (cases/controls or treatment/control)

Question 18

Identify the type of bias:
In choosing controls Investigators excluded women who had had: cholecystectomy, thyroidectomy for thyrotoxicosis, surgery for renal disease, and any cardiac operation because, at the time, reserpine was one of the drugs often used in treating those conditions. The investigators feared that the prevalence of reserpine use in the controls would be artificially high

Answer 18

Exclusion bias

Question 19

What is information bias?

Answer 19

Systematic measurement error or misclassification of the subjects into either risk factor or disease status

Measurement bias

Question 20

What are the types of information bias?

Answer 20

1. Recall
2. Interviewer
3. Observer
4. Leas time

Question 21

What is the main type of bias in case-control studies?

Answer 21

Information bias

Question 22

What is recall bias?

Answer 22

Cases, people who have experienced an event, tend to try to identify some cause and thus are more likely to remember anything suggested as a cause

Exposures that people who did not
experience the event may not even notice

Question 23

Identify the bias

Answer 23

Recall bias

Question 24

What is interview bias?

Answer 24

Interviewers ask leading questions trying to clarify questions when clarification is not a part of study protocol

Question 25

What is observer bias?

Answer 25

The observer may miss an event, diagnosis, or abnormality or think that one exists when it does not Observer misinterprets data Measurement is inaccurate or poor technique

Question 26

**Identify the bias** Repeatedly been documented in studies of blood pressure. Clinicians measuring participants blood pressure using mercury sphygmomanometers have been found to round readings to the nearest whole number.

Answer 26

Observer bias

Question 27

What is lead time bias?

Answer 27

Distortion overestimating the apparent time surviving with a disease caused by moving the time of its diagnosis to an earlier time Same outcome; exaggerated survival time

Question 28

**Identify the bias** Individuals with disease detected by screening receive a diagnosis earlier before signs and symptoms appear. As a consequence, estimates of differences in survival time between people diagnosed from screening and those whose disease is detected after symptoms develop can be biased, as survival time will appear to be longer in screen-detected people if early detection has no effect on the course of disease or if survival time is extended because of earlier detection.

Answer 28

Lead time bias

Question 29

What is attrition bias?

Answer 29

Systematic differences between groups in withdrawals from a study Those who leave a study are likely to be different from those who continue.

Question 30

**Identify the bias** In an intervention study of diet in people with depression, those with more severe depression might find it harder to adhere to the diet regimen and therefore more likely to leave the study.

Answer 30

Attrition bias

Question 31

What is maturation bias?

Answer 31

Occurs when we fail to account for what would have occurred if we done nothing Any biological or psychological process within an individual that systematically varies with the passage of time, independent of specific external events (growing older, wiser, stronger, experienced, tired, hungry)