Section 3: 9 Assessing Validity of Association

Question 1

What are the 7 steps of an research process?

Answer 1

1. research questions
2. hypothesis
3. identify research design
4. data collection
5. presentation of data
6. data analysis
7. interpretation of data

Question 2

What is internal validity?

Answer 2

The results of an observation are correct for the particular group being studied

Question 3

What is external validity?

Answer 3

Do the results of the study apply (“generalize”) to people who were not in the study (e.g. the target
population)?

Question 4

What are some threats to validity in research studies?

Answer 4

• • Random error
• • sample size
• • Systematic error (selection bias, measurement bias, loss to follow-up)
• • Hawthorne Effect
• • Confounding
• • Regression to the mean

Question 5

What are the two questions to be asked when determining if an observed association really exists?

Answer 5

1. Is the association valid?

2. Are there alternative explanations for the association?

Question 6

What are possible alternative explanations for an association?

Answer 6

• Chance (Random Error)
• Bias (Systematic Error)
• Confounding

Question 7

If chance, bias, and confounding have been sufficiently ruled out (or taken into account), does that mean that the valid association observed is causal?

Answer 7

No; it may be a coincidence.

Question 8

What is bias (that might explain an association)?

Answer 8

Systematic error in the design, conduct, or analysis of a study that results in a mistaken estimate of an exposure/disease relationship

Question 9

What are the types of bias possibly found in a study?

Answer 9

1. SELECTION BIAS
2. INFORMATION BIAS
   * Recall Bias
   * Interviewer Bias
   * Reporting Bias
   * Surveillance Bias

Question 10

What is selection bias?

Answer 10

A distortion in a measure of disease frequency or association resulting from the manner in which subjects are selected for the study

Question 11

What is Berkson’s bias?

Answer 11

A form of selection bias that affects hospital-based epidemiology studies. People in hospital are likely to suffer from multiple diseases and engage in unhealthy Whatbehaviours (e.g. smoking). As a result, they are atypical of the population in the community.

Question 12

What is the Healthy Worker Effect?

Answer 12

A form of selection bias that affects
epidemiology studies of workers. Ill and disabled people are likely to be unemployed. The employed (workers) are healthier than other segments of the population. As a result, they are atypical of the population in the community.

Question 13

What is information bias?

Answer 13

Systematic differences in the way in which data on exposure and outcome are obtained from the various study groups.

Question 14

What are some types/sources of information bias?

Answer 14

• • Bias in abstracting records
• • Bias in interviewing
• • Bias from surrogate interviews
• • Surveillance bias
• • Reporting and recall bias

Question 15

What is recall bias?

Answer 15

Study group participants systematically differ in the way data on exposure or outcome are recalled.

Question 16

What type of study is most likely to be affected by recall bias?

Answer 16

case-control studies

Question 17

What is interviewer bias?

Answer 17

Systematic difference in the soliciting, recording, or interpretation of information from study participants

Question 18

What is placebo control?

Answer 18

a method used to maintain observer blindness in randomized trials to avoid interviewer bias

Question 19

What is reporting bias?

Answer 19

Selective suppression or revealing of information such as past history of sexually transmitted disease (reluctance to report an exposure due to attitudes, beliefs, and perceptions)

Question 20

What is wish bias?

Answer 20

a form of reporting bias that may occur among subjects who have developed a disease and seek to show that the disease “is not their fault.”

Question 21

What is surveillance bias?

Answer 21

If a population is monitored over a period of time, disease ascertainment may be better in the monitored population than in the general population

Question 22

What is misclassification bias?

Answer 22

Erroneous classification of the exposure or disease status of an individual into a category to which it should not be assigned

Question 23

How can epidemiologists control bias?

Answer 23

Can only be prevented and controlled
during the design and conduct of a study.
• Choice of a study population
• Methods of data collection
• Sources of case ascertainment and risk
factor information