Lectures #20-21

Question 1

What studies are observational, analytical studies allowing researcher to be a passive observer of natural events occurring in individuals with the disease/condition of interest (cases) who are compared with people who do not have the condition of interest (controls)

Answer 1

Case-Control Studies

Question 2

In case control studies the control group supplies information about what

Answer 2

the expected baseline risk-factor profile in the population from which the cases are drawn

Question 3

In Case control studies the group-assignments are based on

Answer 3

disease status

Question 4

Case-control studies are useful when

Answer 4

studying a rare disease or investigating an outbreak

Question 5

Case-Control studies commonly generate an _____ as measure of association

Answer 5

Odds Ration (OR)

Question 6

What are reasons to select case-control study designs

Answer 6

• unable to “randomize”
  
  • unethical/illegal/otherwise not feasible
• Limited resources
  
  • time/money/subjects
• The disease of interest is rare in occurrence and little is known about its associations/causes
• Prospective exposure data, derived from prospective Cohort study, is difficult/expensive to obtain and/or very time inappropriate

Question 7

Case-control studies are always

Answer 7

Retrospective

Question 8

If you know the outcome/disease status at the time of the study then it is a

Answer 8

retrospective study

Question 9

If the outcome/disease status is not known at the time of the study then the study is

Answer 9

prospective

Question 10

All interventional studies are

Answer 10

prospective

Question 11

Which are cheaper retrospective studies or prospective stuides

Answer 11

retrospective studies

Question 12

What are the strengths of Case Control studies

Answer 12

• Good for assessing multiple exposures of one outcome
• Useful when diseases are rare
• useful in calculating odds and OR’s (associations)
• Less expensive (money/time) than interventional trials and prospective Cohort studies
• Useful when ethical issues limit interventional studies
• Useful for dynamic populations (fluctuating size)
• Useful when disease has a long induction/latent period

Question 13

One of the greatest risks in selection of cases for case control studies is what

Answer 13

misclassification

Question 14

How do researchers select case group in case control study

Answer 14

defined by using accurate, medically-reliable, and efficient data sources

• Applied to all study subjects
• objectively, consistently, accurately, and with Validity
• clinically-supported/definable criteria are best

Question 15

What is the most difficult part of a case control study

Answer 15

Control selection

Question 16

What is the goal when selecting controls

Answer 16

to assess for the presence of an association between exposure and known condition of interest by selecting non-disease individuals from the sample population which produced the cases
- the expectation is that the controls represent the baseline risk of exposure in the general or reference population

Question 17

The way the controls are selected is a major determination in whether

Answer 17

any conclusion is valid (internal validity)

Question 18

If the odds ratio is 1.0 then

Answer 18

then exposure has no effect on the disease/outcome

Question 19

Controls must be selected irrespective of

Answer 19

exposure status

Question 20

you want the control group to be as close to possible with the cases with except for

Answer 20

the presence of disease (outcome) of interest

Question 21

Case-control studies conducted after, or out of, a prospective cohort study

Answer 21

Nested case-control studies

Question 22

What are the 3 kinds of sampling used in nested case-control studies

Answer 22

Survivor sampling
base sampling
risk-set sampling

Question 23

What is survivor sample

Answer 23

sample of non-diseased individuals (survivors) at end of study period

Question 24

What is base sampling

Answer 24

Sample of non-diseased individuals at start of study period

Question 25

what is Risk-set samplin

Answer 25

sample of non-diseased individuals during study period at same time when case was diagnosed

Question 26

What is selection bias

Answer 26

Bias related to the way subjects are chosen for study (usually more of a concern for control selection)

Question 27

What is bias

Answer 27

any factor in the design/execution of a study that causes study groups to be different ultimately leading to a spurious (false) association between variables

Question 28

Selection bias is not a significant issue in what kind of study Case-Control study

Answer 28

Case-Crossover

Question 29

Bias related to the amount/specificity that cases or controls recall past events differently

Answer 29

recall bias

Question 30

What is one way to control for recall bias

Answer 30

use more than one source to answer questions

Question 31

What is individual matching

Answer 31

Matches individuals based on specific patient-based characteristics used when each case has unique and important characteristics

Question 32

Group matching

Answer 32

Proportion of cases and proportion of controls with identical characteristics are matched (ex. 41% male cases and 41% male controls)

Question 33

When doing matching one must not

Answer 33

match on anything that might be a risk factor

Question 34

What is a case-crossover study

Answer 34

used in settings in which the risk of the outcome is increased for only a brief time following the exposure. The period of increased risk following the exposure is termed the hazard period. Cases, serve as their own controls, and the exposure frequency during the hazard period is compared with that form a control period

Question 35

Case-Control studies are always

Answer 35

Retrospective

Question 36

Nested Case-Control studies

Answer 36

Case-Control studies conducted after, or out of, a prospective Cohort study (subjects in cohort study who ultimately develop disease are defined as cases)