SPHL 602 Module 8: Measurement Error

Question 1

Epidemiology

Answer 1

The study of the distribution and determinants of disease frequency in human populations and the application of this study to control health problems

Question 2

Descriptive Epidemiology

Answer 2

The analysis of disease patterns according to the characteristics of person, place, and time

Who is getting the disease? Where is it occurring? How is it changing over time?

Question 3

Bias

Answer 3

A systematic error that results in an incorrect (invalid) estimate of the measure of association between the exposure and disease

Question 4

Ways that bias can be introduced

Answer 4

By the investigator, study participants, or the study design

Question 5

Internal Validity

Answer 5

• There is no bias that is influencing
  measurements, or
• Bias is minimized
• If bias, confounding, and random error have been ruled out as alternative explanations for a study’s findings, the study is deemed internally valid

Question 6

External Validity

Answer 6

• Internal validity must be established

- Results can be generalized beyond the study population

Question 7

What are the two main types of bias in epidemiological research?

Answer 7

1. Selection bias

2. Observation/information bias

Question 8

Characteristics of bias (4)

Answer 8

1. does not mean that the investigator is “prejudiced.”
2. can arise in all study types: experimental, cohort, case-control
3. occurs in the design and conduct of a study.
4. can be evaluated but not fixed in the analysis phase

Question 9

Selection Bias

Answer 9

• An error that results from procedures used
  to select subjects and from factors that
  influence participation in the study
• Occurs when procedures used to select
  study subjects lead to a result different
  from what would have been obtained from
  the entire population targeted for the study

Question 10

In what types of studies is selection bias most likely to occur and why? (2)

Answer 10

In case-control or retrospective cohort studies because the exposure and outcome have already occurred at the time the subjects are selected

Question 11

Where else can selection bias occur?

Answer 11

- In prospective cohort and experimental studies from differential loss to follow-up because this has an impact on which subjects are "selected" for analysis
    \+ Volunteer and non-response bias 
       (Stigma Study)
    \+ Hospital patient bias
    \+ Healthy worker effect

Question 12

Differential loss to follow-up

Answer 12

Drop-out related to outcome status and exposure status

Question 13

Solutions to Selection Bias

Answer 13

1. Use same criteria for selecting cases and controls
2. Obtain all relevant subject records
3. Obtain high participation rates
4. Take into account diagnostic and referral patterns of disease

Question 14

Observation Bias

Answer 14

An error that arises from systematic differences in the way information on exposure on or disease is obtained from the study groups

Question 15

Characteristics of Observation Bias

Answer 15

1. Results in participants who are incorrectly classified as either exposed or unexposed or as diseased or not diseased
2. Occurs after the subjects have entered the study

Question 16

Types of Observation Bias (4)

Answer 16

1. Recall bias
2. Interviewer bias
3. Differential misclassification bias
4. Non-Differential misclassification bias

Question 17

Recall Bias

Answer 17

A type of information bias in which there are differences in the levels of accuracy in the information provided by compared groups

Question 18

Possible result of recall bias

Answer 18

Can result in over-or-under-estimate of the measure of association

Question 19

Ways to address recall bias

Answer 19

1. Use controls who are themselves sick
2. Use standardized questionnaires that
   obtain complete information
3. Mask subjects to study hypothesis

Question 20

Interviewer Bias

Answer 20

A systematic difference in soliciting, recording, or interpreting information that occurs in studies using in-person or telephone interviews

Question 21

In what situations is interviewer bias likely to occur?

Answer 21

1. Whenever exposure information is sought when the outcome is known, or
2. When outcome information is sought when exposure is known

Question 22

Ways to address interviewer bias

Answer 22

1. Mask interviewers to study hypothesis and disease, or exposure status of subjects
2. Use standardized methods of outcome (or exposure) ascertainment

Question 23

Misclassification Bias (Measurement Error)

Answer 23

Subject’s exposure or disease status is erroneously classified

Question 24

Types of Misclassification Bias

Answer 24

1. Non-Differential misclassification bias

2. Differential misclassification bias

Question 25

Non-Differential Misclassification Bias

Answer 25

• inaccuracies with respect to disease classification are independent of exposure, or
• inaccuracies with respect to exposure are independent of disease

Question 26

Problem caused by Non-Differential Misclassification Bias

Answer 26

Will bias towards the null if the exposure has two categories; makes the groups more similar

Question 27

Ways to Address Non-Differential Misclassification Bias

Answer 27

1. Use multiple measurements

2. Most accurate source of information

Question 28

Random Error

Answer 28

the probability that the observed result is due to “chance,” an uncontrollable force that seems to have no assignable cause

Question 29

Loss to Follow-Up

Answer 29

A type of selection bias that occurs when subjects whose outcomes are unknown drop out of a cohort study because they can no longer be located or because they no longer want to participate

Question 30

Healthy Worker Effect

Answer 30

A type of selection bias that occurs when the general population is chosen as a comparison (control) group in an occupational cohort study

Question 31

In what types of studies can recall bias occur?

Answer 31

1) In a cohort study if cases are more or less likely than
controls to recall and report prior exposures

2) In a cohort study if exposed subjects are more or
less likely than unexposed subjects to recall and
report subsequent diseases

Question 32

Control Selection Bias

Answer 32

Selection of an inappropriate control group in a case-control study

Question 33

Self-Selection Bias

Answer 33

1) An error occurring in a case-control study arising from
refusal or nonresponse by participants related to both
exposure and disease, or

2) Agreement to participate that is related to both the
exposure and disease

Question 34

Differential Surveillance, Diagnosis, or Referral

Answer 34

A type of selection bias that can result from a tendency to hospitalize patients differentially based on their exposure status