Case Control Studies

Question 1

compare and contrast case control versus cohort studies

Answer 1

with case control studies, you are handed an outbreak and try to find the cause with questionnaires that grow more specific (outcome known before exposure) while with cohort studies you send out a questionnaire to determine the group you are going to study based on their exposure to a certain risk factor, then follow them to see the outcome

Question 2

what is the worst study design to determine causality?

Answer 2

case reports

Question 3

what are the 3 best study designs to determine causality?

Answer 3

random controlled trials, cohort studies, case-control studies

Question 4

what can you measure with a cohort study that you usually don’t know with a case-control study?

Answer 4

level of exposure

Question 5

what are the 2 types of cohort studies?

Answer 5

1. prospective
2. retrospective

Question 6

how are retrospective cohort studies usually performed and what is an advantage of this type of study?

Answer 6

performed by data-mining and you can add more risk factors or layers than a prospective cohort study

Question 7

define a case-control study

Answer 7

an analytic epidemiologic research degisn in which the study population consists of groups who either have (cases) or do not have a particular health problem or outcome (control)

Question 8

how does the investigator look in a case control study?

Answer 8

looks back in time to measure exposure of the study subjects, then compares exposure among cases and controls to determine if the exposure could account for the health condition of the cases

Question 9

give 7 characteristics of case-control studies

Answer 9

1. observational/non-experimental
2. occasionally exploratory
3. explanatory (analytical)
4. restrospective
5. effect to cause (what made them sick?)
6. both exposure and disease have already occurred
7. uses comparison group (controls)

Question 10

give an overview of the design of case control studies

Answer 10

the investigator selects cases with the disease and appropriate controls without the disease and obstains data regarding past exposure to possible etiologic factors in both groups; the investigator then compares the frequency of exposure of the two groups

Question 11

what groups compose the cases in a case control study?

Answer 11

those who get the disease from exposed and not exposed

Question 12

what groups compose the controls in a case control study?

Answer 12

those who do not get the disease from exposed and not exposed

Question 13

what do we ask concerning odds ratios in case control studies?

Answer 13

we ask whether certain exposures are more common among those with disease

Question 14

describe the sampling frame of a typical case control study

Answer 14

typically sampling only a portion of the individuals that were potentially exposed

Question 15

what does relative risk help determine in a case control study?

Answer 15

relative risk helps to determine whether the incident of disease is associated with certain exposures

Question 16

what do we rely on in case control studies to determine whether exposure to a risk factor is more common among cases versus controls and why?

Answer 16

we have to rely on odds ratios (chances) because likely only sampling a portion of the population that was exposed (called the reference population)

Question 17

give 7 sources of controls in case control studies

Answer 17

1. population of a defined area
2. hospital patients
3. probability sample of total population
4. neighbors
5. friends or associates of cases
6. siblings, spouses, relatives
7. other

Question 18

what is bias?

Answer 18

any systematic error in study design that results in an incorrect estimation of the association between exposure and risk of disease

Question 19

what is information bias?

Answer 19

when differences in the way exposure or outsome are measured between controls and disease groups and observers are privy to the outcome and influence data

Question 20

how do you avoid information bias? (3)

Answer 20

1. use blind studies
2. struct protocols
3. standardized questionnaires

Question 21

describe recall bias

Answer 21

the individuals being questioned have different levels of recall; so cases (thanks to the trauma of illness) are likely to better recall exposures than controls

Question 22

what does recall bias result in?

Answer 22

over or under estimation of associations between exposure and outcome

Question 23

describe selection bias

Answer 23

poor selection of controls, in which there are differences beyond exposure

Question 24

give an example of selection bias

Answer 24

if you are conducting a study on poverty and measles, but fail to conisder who is vaccinated against measles versus who is not

Question 25

what is confounding?

Answer 25

when another variable (outside the one being considered) may influence the outcome of a disease

Question 26

give an exmaple of confounding

Answer 26

if it is stated that alcoholics are more likely to develop lung cancer, so alcohol must cause lung cancer; is ignoring the fact that alcoholics are just more likely to smoke than non-alcoholics

Question 27

give 2 effects of confounding

Answer 27

1. can mislead the investigator to make associations, or miss associations, between a risk factor and a disease outcome when none or one really exists
2. can cause an over or under estimation of a risk factor’s effect

Question 28

give 4 advantages of case control studies

Answer 28

1. cheap, easy, and quick
2. multiple exposures can be examined
3. rare diseases and diseases with long latency can be studied
4. suitable when randomization is unethical (like the effects of drinking alcohol during pregnancy)

Question 29

give 8 disadvantages of case control studies

Answer 29

1. case and control selection can be troublesome
2. subject to multiple biases
3. direct incidencce estimation is not possible
4. temporal relationship is not clear
5. if incidence of exposure is high, it is difficult to show the differences between cases and controls
6. not easy to estimate attributable fraction
7. reverse causation is a problem in interpretation
8. multiple outcomes can not be studied (cohort studies can study this though!)