Cohort Studies

Question 1

what do cohort studies do?

Answer 1

cohort studies define and measure the risk factor (exposure) and then evaluate the outcome in a suitable demographic group over time

Question 2

what can the outcome be in a cohort study? (2)

Answer 2

outcome can be the presence or absence of a disease associated with a certain risk factor

Question 3

can you evaluate multiple risk factors with a single cohort study?

Answer 3

no; would then have to be separate studies for each risk factor

Question 4

what can you do with a cohort study that you can’t do with a case control study?

Answer 4

can pick dose or population

Question 5

what is the major difference between cohort and case control studies?

Answer 5

in cohort studies the population being studied is well-defined in demographics and numbers

Question 6

what are the 2 types of cohort studies and what do they depend on?

Answer 6

can be prospective or restrospective, depending on the availability of data

Question 7

what is an advantage of retrospective cohort studies?

Answer 7

save time if data is available

Question 8

in what direction do you work in a case control study?

Answer 8

from outcome backwards to identify exposure

Question 9

in what direction do you work in a cohort study?

Answer 9

from exposure forward to see the outcome

Question 10

what is the ideal scenario for the control group in a cohort study regarding exposure to the risk factor? what complicates this? how do you determine this?

Answer 10

ideally the control group should have no exposure to risk factor; is complicated to determine is the group is only known through published data; conduct personal interviews if you can

Question 11

what is the key point regarding cohort studies?

Answer 11

the presence or absence of the risk factor is determined BEFORE the outcome occurs

Question 12

what is the basic idea of cohort studies?

Answer 12

see if those WITH the risk factor develop MORE disease than those WITHOUT the risk factor

Question 13

compare the odds ratio to the relative risk in cohort studies

Answer 13

odds ratio is often higher than relative risk due to smaller populations and a larger margin of error

Question 14

what are person years?

Answer 14

adjusts for the amount of time that any individual member of the cohort’s data is available

Question 15

why are person years helpful?

Answer 15

some individuals are in the study longer than others, so it is better to evaluate the number of person years rather than the number of people in the study

Question 16

when are person years very important and helpful?

Answer 16

with long term regional studies as people are more likely to drop out, move, etc.

Question 17

what is reverse causality?

Answer 17

confounding by disease

Question 18

what is the problem with reverse causality, or confounding by disease?

Answer 18

associations between risk factors and some disease outcome sare confounded by pre-existing comorbidities (tricky)

Question 19

what should you ask to determine if selection bias is present in a cohort study?

Answer 19

are participants in exposed and unexposed groups similar in all ways except for the exposure?

Question 20

what should you ask to determine if selection bias is present in a case control study?

Answer 20

are cases and controls similaar in all important aspects except for the disease in question?

Question 21

what should you ask to determine if information bias is present in a cohort study?

Answer 21

is information about the outcome obtained in the same way for those exposed and those exposed?

Question 22

what should you ask to determine if information bias is present in a case control study?

Answer 22

is information about exposure gathered in the same way for cases and controls?

Question 23

what should you ask to determine if confounding is present?

Answer 23

could the results be accounted for by the presence of a factor associated with both the exposure and the outcome but not directly invovled in the causal pathway>

Question 24

what are 3 features to look for in a cohort study?

Answer 24

1. what steps were taken to minimize information bias?
2. how complete was the followup of both groups?
3. were potential confounding factors sought and controlled for in the analysis?

Question 25

compare and contrast cohort versus case control study (5)

Answer 25

1. cohorts tend to be long term and require significant preliminary planning
2. cohorts are less useful in the stuudy of diseases of low prevalence or exposure
3. cohort deals better with confounding and bias
4. in cohorts, the strength of association is typically stronger for relative risk than odds ratios
5. with case-control, you can extrapolate the results beyond the study group

Question 26

why can you extrapolate case control studies beyond the study group?

Answer 26

1. the demographic latitudes inherent in control group formation
2. the additional veriation built into the confidence interval by including factorials for the control groups

Question 27

what are clinical trials?

Answer 27

cohort studies in which the exposure to the effector is controlled

Question 28

what are the 4 types of clinical trials?

Answer 28

1. placebo-controlled
2. single blind
3. doublle blind
4. triple blind

Question 29

what are the 4 methods by which a diagnosis can be made?

Answer 29

1. quantitative
2. qualitative
3. subjective
4. objective

Question 30

what do sensitivity and specificity measure

Answer 30

how good a test is at detecting binary features of interest (disease/no disease)

Question 31

how do you calculate senstivity?

Answer 31

(those who test positive) divided by (those who are positive for the disease)

Question 32

how do you calculate specificity?

Answer 32

(those who test negative) divided by (those who are negative for the disease)

Question 33

how is the true disease status usually determined?

Answer 33

by some gold standard method

Question 34

describe the relationship between sensitivity and specificity for a specific test

Answer 34

for a specific test, sensitivity increases as specificity decreases and vice versa

Question 35

what is sensitivity?

Answer 35

the capacity of a test to correctly idenitfy TRUE POSITIVES

Question 36

what happens to the number of false negatives as sensitivity increases

Answer 36

the greater the sensitivity, the smaller the number of unidentified false positives

Question 37

what is specificity?

Answer 37

the capacity of a test to correctly exclude individuals who are free of the disease (FLASE NEGATIVES)

Question 38

what happens to false positives as specificity increases?

Answer 38

the greater the specificity, the fewer false positives will be included

Question 39

what is positive predictive value?

Answer 39

the probability of the disease being present among those with positive diagnostic results

Question 40

what is negative predictive value?

Answer 40

the probability of the disease being absent among those whose test results were negative

Question 41

what is Bayes Theorem?

Answer 41

used to compare one lab test to a reference lab with the gold standard test

Question 42

what is misclassification?

Answer 42

the placement of subjects into inappropriate groups or classifications

Question 43

when does random misclassification occur?

Answer 43

when the means by which we measure risk factors or disease are not perfect

Question 44

when does non-random misclassification occur?

Answer 44

when exposure or disease status influences group assignment

Question 45

what do misclassifications usually insert into data?

Answer 45

typically insert unwarranted bias, but can be corrected for if detected