Bias And Study Errors

Question 1

Bias And Study Errors - recruiting participants

Answer 1

Selection bias

Question 2

Bias And Study Errors - performing study

Answer 2

1. Recall bias
2. Measurement bias
3. Procedure bias
4. Observer-expectancy bias

Question 3

Bias And Study Errors - Interpreting results

Answer 3

1. Confounding bias

2. Lead time bias

Question 4

Selection bias (type and definition)

Answer 4

Type: Recruiting participant bias

Error in assigning subjects to study group resulting in an unrepresentative sample. Most commonly a sampling bias

Question 5

Selection bias examples

Answer 5

1. Berkson bias (from hospitals)
2. Healthy worker effects
3. Non-response bias

Question 6

Strategy to reduce selection bias

Answer 6

1. Randomization

2. Ensure the choice of the right comparison/reference group

Question 7

Berkson bias

Answer 7

Type of selection bias

Study population selected from hospital is less healthy than general population

Question 8

Healthy worker effect

Answer 8

Type of Selection bias

Study population is healthier than general population

Question 9

Non-response bias

Answer 9

Type of Selection bias

Participating subjects differ from nonrespondents in meaningful ways

Question 10

Recall bias (type and definition)

Answer 10

Type: performing study

Awareness of disorder alters recall by subjects. Common in retrospective studies

Question 11

Recall bias example

Answer 11

Patients with disease recall exposure after learning of similar cases

Question 12

Recall bias strategy to reduce

Answer 12

Decrease time from exposure to follow up

Question 13

Measurement bias (type and definition)

Answer 13

Type: performing bias

Information is gathered in a way at distorts it

Question 14

Measurement bias example

Answer 14

Miscalibrated scale consistently overstates weights of subjects

Question 15

Measurement bias strategy to reduce

Answer 15

Use objective, standardized and previously tested method of data collection that are planned ahead of time

Question 16

Procedures bias (type and definition)

Answer 16

Performing study

Subjects in different group are not treated in the same way

Question 17

Procedure bias example

Answer 17

Patients in treatment group spend more time in highly specialized hospitals units

Question 18

Procedure bias strategy to reduce

Answer 18

Blinding and use of placebo reduce influence of participant and researchers on procedures and interpretation of outcomes as neither are aware of group allocation

Question 19

Observer-expectancy bias (type and definition)

Answer 19

Type: Performing study
Researchers belief in the efficacy of the treatment changes the outcome of that treatment (aka Pygmalion effect, self-fulfilling prophesy)

Question 20

Observer-expectancy bias example

Answer 20

If observer expects treatment groups to show signs of recovery, then he is more likely to document positive outcomes

Question 21

Observer-expectancy bias strategy of reduction

Answer 21

Blinding and use of placebo reduce influence of participant and researchers on procedures and interpretation of outcomes as neither are aware of group allocation

Question 22

Bias And Study Errors types

Answer 22

1. Recruiting participants
2. Performing study
3. Interpreting results

Question 23

Interpreting results bias types

Answer 23

1. Comfounding bias

2. Lead times bias

Question 24

Comfounding bias (types and definition)

Answer 24

Type: Interpreting bias
When factor is related to both exposure and outcomes, but not to the causal pathway –> factor distorts or confuses effects on outcome

Question 25

Confounding bias example

Answer 25

Pulmonary disease is more common in coal workers than the general population. However, people who work in coal mines also smoke more frequently than the general population

Question 26

Confounding bias strategy of reduction

Answer 26

1. Multiple/repeated studies
2. Crossover studies (subjects act as their own controls –> persons in group 1 receive the drug and group 2 placebo. Later they swich)
3. Matching (patient with similar characteristics in both treatment and control groups)
4. Restriction
5. Randomization

Question 27

Lead-times bias type and definition

Answer 27

Type: interpreting results

Early detection is confused with increased survival

Question 28

Lead time bias example

Answer 28

Early detection makes it seems as though survival has increased, but the natural history of the disease has not changed

Question 29

Lead time bias strategy of reduction

Answer 29

Measure “back end” survival (adjust survival to the severity of disease at the time of diagnosis)

Question 30

Recall bias is common in

Answer 30

Retrospective bias

Question 31

Observer expectancy bias is also called

Answer 31

1. Pygmalion effect

2. Self-fulfilling prophecy

Question 32

Pygmalion effect is aka

Answer 32

1. Observer expectancy

2. Self-fulfilling prophecy

Question 33

Crossover studies

Answer 33

subjects in group 1 receive the drug and group 2 placebo. Later they switch –> subjects act as their own control

Question 34

types of bias - groups

Answer 34

1. recruiting participants
2. performing study
3. interpreting results