Module 8 (Ch.9)

Question 1

In a case-control study, people with a health outcome (disease) are compared to those without the health outcome (disease). ________ are people who have disease. ________ are people who don’t have disease.

Answer 1

In a case-control study, people with a health outcome (disease) are compared to those without the health outcome (disease). Cases are people who have disease. Controls are people who don’t have disease.

A case-control study allows you to relate exposure to a disease

Question 2

Why do some people criticize case-control studies?

Answer 2

They say that the logic (looking at an effect to find a cause) seems backwards and that these studies seem more prone to bias than other designs

Question 3

Which of the following is not a reason to choose a case-control study design:
* Don’t have exposure data
* Don’t have time in your schedule to do a randomized trial
* Disease of interest is rare
* Disease has long induction and latent period
* Little is known about the disease
* Underlying population is dynamic

Answer 3

Don’t have time in your schedule to do a randomized trial is not a reason to do a case-control study. The others in the list are good reasons for a case-control study.

Question 4

It is best to use all available evidence to define with as much accuracy as possible the true cases of disease. True or False?

Answer 4

True

Question 5

if________ criteria is used for cases, most cases will be captured (but not all) and many people who do not have the disease will be misclassified.

Answer 5

if nonspecific criteria is used for cases, most cases will be captured (but not all) and many people who do not have the disease will be misclassified.

Question 6

If ________ of a criteria for cases is used, fewer cases will be captured and the sample size will be smaller.

Answer 6

If too restrictive of a criteria for cases is used, fewer cases will be captured and the sample size will be smaller.

Question 7

what are good sources for identifying cases of disease?

Answer 7

• hospital or clinic patient rosters
• death certificates
• special reporting systems
• cancer registries
• birth defect registries

Question 8

Researchers who study the causes of disease are most interested in the ____________ (incident or prevalent) cases because they are interested in the factors that lead to developing the disease.

Answer 8

Researchers who study the causes of disease are most interested in the incident cases because they are interested in the factors that lead to developing the disease.

Question 9

________ are a sample of the source population
that gave rise to the cases

Answer 9

Controls are a sample of the source population
that gave rise to the cases

Question 10

Cases and controls should represent the same
________ population

Answer 10

Cases and controls should represent the same
source population

Question 11

Should exposure status play a role in who is
chosen as a control?

Answer 11

No, exposure status shouldn’t determine who is chosen as control

Question 12

What is the “the would criterion” in a case-control study design?

Answer 12

the “would criterion” says if a member of the control group actually had the health condition under
study, they should end up as a case in your study.

Question 13

Control groups are often selected from a hospital population (when cases are selected from a hospital population) and controls are selected from ____________ (when the cases are from a defined geographic location).

Answer 13

Control groups are often selected from a hospital population (when cases are selected from a hospital population) and controls are selected from the general population (when the cases are from a defined geographic location).

Question 14

What are advantages and disadvantages to using hospital patients as controls?

Answer 14

Advantages
* Easy access
* Less bias

Disadvantages
* Their own illness (it can be okay if the illness has no relation to the risk factors under study
* It can be difficult to make sure that you only choose controls that have the same referral pattern as the cases (acute condition vs acute condition, chronic vs chronic)

Question 15

What are advantages and disadvantages to using people from the general population as controls?

Answer 15

Advantage
* Selected from same population as cases

Disadvantages
* Time consuming
* expensive
* May remember exposures differently than cases (recall bias)

Question 16

How do you recruit non-hospitalized controls?

Answer 16

• Door-to-door recruiting
• Telephone recruiting
• Other sources
• School enrollment lists
• Insurance company lists
• Selective service registry

Question 17

Matching controls to cases helps to ensure similarity in the two groups, which should be similar except for ____________.

Answer 17

Matching controls to cases helps to ensure similarity in the two groups, which should be similar except for ____________.

Question 18

Matching controls to cases helps to ensure similarity in the two groups

Answer 18

____________ controls to cases helps to ensure similarity in the two groups

Question 19

( Group matching or individual matching ) is when you select cases and then match controls to match proportions.

Answer 19

Group matching is when you select cases and then match controls to match proportions.

Question 20

(Group matching or individual matching) is when you individually match each control to a case creating matched pairs

Answer 20

Individual matching is when you individually match each control to a case creating matched pairs

Question 21

What are some problems with matching?

Answer 21

• Trying to match by too many
• If you match by a characteristic, then you can’t study that characteristic

Question 22

What is recall bias?

Answer 22

Some people may have better memories of
certain events than others
* Cases may have spent time thinking of their
own potential exposures and may recall these
more than a control

Question 23

what measure of association is used for case-control studies?

Answer 23

Odds ratio - which tells us the odds of having a positive exposure history

Question 24

The definition of odds is the ratio of the probability of
an event occurring to that of it not occurring. True or False?

Answer 24

True

Question 25

What is the formula for the odds ratio?

Answer 25

OR = Odds that an exposed person is a case / Odds that an unexposed person is a case

OR = ad/bc , OR = a/b divided by c/d

Question 26

Interpreting odds ratio

• What does it mean if an OR is equal to 1?
• What does it mean if an OR is greater than 1?
• What does it mean if an OR is less than?

Answer 26

• OR = 1: There is no evidence of an association between exposure and health outcome
• OR > 1: There is a positive association between exposure and a health outcome (it may
  be causal)
• OR < 1: There is a negative association between exposure and health outcome(The
  exposure may be protective)

Question 27

What are some strength of case-control studies?

Answer 27

• Efficient for rare diseases and diseases with long induction and latent period
• Can evaluate many risk factors for the same disease

Question 28

What are some weaknesses of case-control studies?

Answer 28

• Inefficient for rare exposures
• Vulnerable to bias because of retrospective nature of study
• May have poor information on exposure because retrospective
• Difficult to infer temporal relationship between exposure and disease

Question 29

Compare case-control studies to cohort studies

Answer 29

Cohort studies compare people with exposure to people
without exposure. Case-control studies compare people with disease to people without disease.

Question 30

What are cross sectional studies?

Answer 30

• Exposure and health outcome outcome are
  identified simultaneously for a study subject
• Snapshot of the population

Question 31

What are ecological studies?

Answer 31

These are studies of the characteristics of
groups