Lecture 7: Bias and confounding Flashcards

1
Q

What is Bias in biostatistics?

A

Bias is any systematic error in design/implementation of a study
•Systematic error in selecting participants
•Systematic error in data collection

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Wha is the effect of bias?

A

It creates the tendency to overestimate or underestimate a measure of association.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the types of bias?

A

Random error

Systematic error:

  • information bias
  • selection bias
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is Selection bias?

A
  • Errors introduced when the study population does not represent the target population
  • Systematic difference between those included in a study and those who are not
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How do you reduce selection bias?

A

The most effective method to minimise selection bias in intervention studies is random allocation to treatment and control groups.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is Volunteer or Non- response bias?

A

Typically occurs in surveys/observational studies, where individuals decide whether or not to participate.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the Healthy worker effect ?

A

Occurs in occupational cohort studies or in studies comparing working to non-working populations.

The effect:

  • Workers have lower rate of disease than non-workers
  • Lower mortality in the employed population compared to the general population.
  • Comparison of workers to non-workers may underestimate the health effects of occupational exposures
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is Neyman’s bias .

A

Neyman Biasis a selection bias where the very sick or very well (or both) are erroneously excluded from a study.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the effects of Neyman bias?

A
  • Excluding patients with severe disease will make treatment effective
  • Excluding patients who have recovered will make conditions lookmoresevere.

It affects studies on long-term conditions e.g. HIV or tuberculosis. Less of a problem with acute conditions.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is Attrition bias?

A

Loss to follow up

It can occur in Cohort studies and randomized controls trials (RCT’s) which involve following people over a certain period of time

Those that are lost to follow up may be different from those who complete the study

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is information (measurement) bias?

A

Information bias is a systematic error in exposure assessment or outcome assessment

Biased data (even with random sample)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is Recall bias?

A

Error due to differences in accuracy or completeness of recall to memory of past events or experiences.

Respondents memory vary according to whether they have experienced the outcome
- Cases with disease are more likely to recall the possible cause of their illness than healthy people.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is Interviewer bias?

A

Interviewer bias occurs when there are systematic differences in the way information is collected for the groups being studied

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How can interviewers influence respondents’ answers?

A

Structure of questions – e.g. putting emphasis on questions, use of gestures.

The interview situation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is Observer bias?

A

Occurs when observers are not blinded to exposure or disease status

Observers may have preconceived expectations of what they should find in an examination

Example: Radiologist aware of a patient’s smoking status may look more critically at abnormalities in X-ray.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the Hawthorne effect?

A

Alteration in behaviour when subjects know they are being studied.

17
Q

How does Controlling for bias occur?

A
  • Ensure sample selection is random
  • Measure and control all variables related to health behaviour
  • Set up strict guidelines for data collection:
    Use standardised questionnaires, train interviewers and observers, preferably use more than one observer.
  • Institute Blinding/masking where appropriate:
    Blinding prevents interviewers or observers (and some times subjects) from knowing case/control status, treatment allocation, or exposure status of study subjects.
  • Use an appropriate method for data collection
    E.g. for socially sensitive questions, such as alcohol and drug use or sexual behaviours, use a self-administered questionnaire instead of an interviewer.
  • Build in methods to minimise loss to follow-up:
    Recruit people who can easily be tracked
    Use of incentives
18
Q

Define confounding

A

Lack of comparability: when certain background factors differ between groups being compared.

A mixing of effects: A situation in which the apparent effect of an exposure on risk is explained by other factors, resulting in a distortion of the true relationship

19
Q

What is lack of comparability in confounding?

A

when certain background factors differ between groups being compared.

20
Q

What is a mixing of effects in confounding?

A

A situation in which the apparent effect of an exposure on risk is explained by other factors, resulting in a distortion of the true relationship

21
Q

What are Confounders?

A

Factors or variables that cause confounding

22
Q

What are the conditions to be a Confounder?

A

Associated with the exposure

Associated with the outcome

Not on the causal pathway between the outcome and exposure

23
Q

How to deal with confounding in design and statistical analysis?

A

Randomisation

Matching

Restriction

Stratification

Multi-variate regression analysis

24
Q

Bias refers to errors in the design or conduct of a study that can result in false conclusions

True or false?

25
Selection bias can occur when the study sample does not reflect the population of interest True or false?
True
26
Information bias can occur when the method used in collecting study data could lead to inaccurate responses or measurements True or false?
True
27
Confounding can be minimised at ?
Design stage- randomisation Analysis stage- stratification, regression analysis