Case-Control Studies

Question 1

Case-control studies are conducted in a ________ fashion

Answer 1

retrospective

Question 2

What do case control studies commonly generate when studying a rare disease? (2 things)

Answer 2

an Odds of exposure and then an Odds ratio

Question 3

When you see the phrase “randomized” what does that mean? what about the phrase “randomly selected”?

Answer 3

“randomized” = interventional study design

“randomly selected” = doesn’t necessarily mean it’s an interventional study design

Question 4

in a case-control study, what are the group assignments based on?

Answer 4

disease status

Question 5

describe what is known before a case-control study begins, and what should be discovered when reviewing the collected data AFTER the study is over

Answer 5

at the beginning all you know is “who does and does not have the disease/outcome” (A+C and B+D)

at the end, you should know who was exposed out of each comparison group (A, C, B, and D individually)

Question 6

What is the most difficult group to select in a case-control study? why?

Answer 6

the controls

they must represent the baseline as accurately as possible with the highest possible amount of exchangeablity

Question 7

Controls must be selected irrespective of _____ status

Answer 7

exposure

Question 8

what effect does selection bias have on a case control study?

Answer 8

it decreases the validity of a study

Question 9

Cite and delineate examples of the 3 sources for selecting controls for a case-control study.

Answer 9

Population (state/community/neighborhood): can be obtained randomly or another method

Institutional/organizational/provider: cannot select based off of exposure (duh)

Spouse/relatives/friends: genetic, environmental, or socioeconomic similarities

Question 10

if there is an outbreak that you are conducting a case-control study for, how should you select the control group?

Answer 10

be sure that they are associated with the outbreak in the same way as the cases (ex. they may have all been at the same convention)

Question 11

what is the only type of case-control study where subjects serve as an individual who has been exposed and not exposed within the same study? how can this be?

Answer 11

case-crossover design studies.

outbreak investigations with multiple exposures being studied OR situations with brief (acute) change in the risk of the outcome

Question 12

What type of case-control design can adequately address the issue of temporality within a study?

Answer 12

case-crossover designs (still a type of case-control study)

Question 13

When using matching schemes to set up a study, what should kind of characteristics should never be used to match?

Answer 13

anything that might be a risk factor.

Question 14

When matching is being used in a study, what is the normal ratio that is used to match cases and controls? would it every be any different? why?

Answer 14

1:1 (bc thats even, duh)

If it is different than 1:1 then the ratio would be higher in an attempt to “average out their differences”

Question 15

list the strengths of a case-control study design (6 of them)

Answer 15

Good for assessing multiple exposures of one outcome

Useful study for rare diseases

Determines associations (not causation)

Inexpensive in terms of money/time (when compared to interventional and prospective cohort studies)

Useful when ethical issues limit interventional studies

Useful when the disease has a long induction/latent period

Question 16

For case-control study designs. list 4 reasons why you should choose this design over a different study design.

Answer 16

If you are unable to force group allocation

have limited resources

the disease of interest is rare

prospective data is difficult to obtain

Question 17

2. Define a case-control studies in terms of being observational and analytical.

Answer 17

They are observational studies where the researcher plays a passive observational role that studies the natural events occurring in the case and control groups of subjects

not analytical enough to determine causation. strong associations are the extent of conclusions that can be drawn from this study

Question 18

3. Cite and delineate examples of how to define a case and control when conducting a case-control study.

Answer 18

Disease status determines if the subject is a case or control (already in brain scape)

Cases are selected using criteria that is defined by the investigator and should use accurate, consistent, clinically supportable criteria

Question 19

7. Describe the purpose & types of matching and benefits when conducting a case-control study.

Answer 19

Individual matching: matches individuals based on specific, patient-based characteristics
(Useful for controlling confounding characteristics)

Group matching: proportion of cases and proportion of controls with identical characteristics are matched evenly (this requires that cases be selected first)

Question 20

9. Define the term “nested” as it relates to a case-control study and cite its advantages.

Answer 20

Nested: case-control studies conducted AFTER (prospective) a previous study when the diseased group and from one study is used in a new, different study

Advantages: used to evaluate other exposures