Case-Control Studies

Question 1

case-control studies

Answer 1

observational studies allowing researcher to be a passive observer of natural events occurring in individuals with the disease of interest compared to people who do not have the disease

Question 2

group assignments of case-control studies

Answer 2

group assignments are based upon your disease status

diseased = group of interest
no disease = control

Question 3

case-control studies are useful when …..

Answer 3

studying a rare disease or investigating an outbreak

Question 4

case-control: randomization

Answer 4

do not randomize people into groups

take the population and just randomly select people to include but their group allocation is decided by their disease state

Question 5

in case-control we are looking at…….. (data)

Answer 5

odds of exposure for each group and an odds ratio

commonly use a 2x2 table to compare the data

Question 6

reasons to select a case-control design

Answer 6

1. unable to force group allocation
2. limited resources
3. disease of interest is rare
4. prospective exposure data is hard to obtain

Question 7

unable to force group allocation

Answer 7

unethical

not feasible

Question 8

limited resources

Answer 8

time
money
subjects

Question 9

disease of interest is rare

Answer 9

in occurrence

little is known about it’s associations or causes

Question 10

prospective exposure data is difficult to obtain

Answer 10

expensive

time inappropriate

Question 11

case-control studies are classically _______ studies

Answer 11

retrospective studies
data is already collected, all has happened in the past
ex. any long term cancer

typically know the outcome of interest

Question 12

strengths of case-control studies

Answer 12

• good for assessing multiple exposures of one outcome
• good for rare diseases
• good for determining associations (not causes)
• less expensive than interventional/prospective studies
• less ethical issues
• good for diseases w/ long induction/latent periods

Question 13

weaknesses of case-control studies

Answer 13

1. can’t determine causes
2. impacted by confounders
3. retrospective-cannot control for variables or contamination
4. impacted by biases - selection and recall bias
5. may only have limited data available due to being retrospective

Question 14

selection of cases is defined by _______

Answer 14

the investigator using accurate, medically reliable data sources

classifying patients correctly is ideal but misclassification is present

Question 15

new term for case definition

Answer 15

diagnostic criteria

Question 16

all else being equal, the outcome if something didn’t occur

Answer 16

recall counterfactual theory

requires assumption of exchangeability to allow comparability

Question 17

most difficult part of case-control studies is

Answer 17

picking the controls

Question 18

goals of control selection

Answer 18

to assess for the presence of an association between exposure and known condition of interest by selecting non-diseased individuals from the same population which produces the cases

Question 19

expectation of the controls

Answer 19

that they represent the baseline risk of exposure in the population

Question 20

control subjects cannot be selected upon

Answer 20

because of their exposure

researcher cannot look at a subjects exposure before allocating them as a control

Question 21

the way controls are selected is a major determinant of …….

Answer 21

1. validity of conclusions
2. internal validity
3. selection bias

Question 22

differences between case and control groups

Answer 22

want the groups to be as equal as possible except that the control subjects do not have the disease

Question 23

if the exposure truly has no effect, then ……

Answer 23

the odds will be exactly the same for both groups

OR = 1.0

Question 24

controls must be selected ……

Answer 24

irrespective of exposure status

Question 25

selection of controls can come from several sources:

Answer 25

1. randomly obtained from the population
2. institutional/ organization/ provider of care
3. spouse/ relatives/ friends

Question 26

how to select the control group for studies on an outbreak

Answer 26

people who participated in the same event that caused the outbreak but did not get the actual illness

Question 27

an individual can function as both an exposed individual and an unexposed individual in the same study

Answer 27

the case-crossover design

because they are looking at different exposures

Question 28

the only case-control design able to adequately attempt to address the issue of ______ .

Answer 28

case-crossover design

issue of temporality

Question 29

case-crossover study

Answer 29

a case-control study (observational)

finds people who are cases and finds a temporally close earlier time period in their life when they weren’t doing the exposure so didn’t have the event

Question 30

nested case-control study

Answer 30

a case-control study nested/comes from a study that is already done. from a cohort or interventional study.

comes from another study but set up as a normal case-control study

can be used to evaluate other exposures

Question 31

selection of controls used for nested case-control studies

Answer 31

1. survivor sampling
2. base sampling
3. risk-set sampling

Question 32

survivor sampling

Answer 32

sample of non-diseased individuals at end of the study period

for control subjects in nested case-control studies

Question 33

base sampling

Answer 33

sample of non-diseased individuals at start of study period

for control subjects in nested case-control studies

Question 34

risk-set sampling

Answer 34

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

for control subjects of nested case-control studies

Question 35

another term for risk-set sampling

Answer 35

risk-analysis sampling

Question 36

common biases in case-control studies

Answer 36

1. selection bias — how subjects were chosen

2. recall bias — is subjects are required to recall information that will effect the study

Question 37

matching

Answer 37

1:1 typically in case:control but can be higher

can be individual or group matching

Question 38

individual matching

Answer 38

matching individuals based on specific patient-based characteristics

Question 39

what is individual matching useful for?

Answer 39

controlling confounding characteristics

Question 40

group matching

Answer 40

proportion of cases and proportion of controls with identical characteristics are matched

this requires cases to be selected first

Question 41

what does group matching require

Answer 41

case subjects to be selected first

Question 42

when matching, never match anything that ____ .

Answer 42

could be a risk factor