Lecture 5 - Observational Studies II

Question 1

In cohort studies _________ is assessed at baseline

Answer 1

exposure

Question 2

In cohort studies, participants are ______ at baseline

Answer 2

disease-free

Question 3

What are two other terms for prospective

Answer 3

longitudinal, concurrent

Question 4

What are two other terms for retrospective

Answer 4

historical, nonconcurrent

Question 5

for cohort studies, _______ is measured before ____

Answer 5

exposure is measured before outcome

Question 6

When are prospective studies used?

Answer 6

time btw exposure and disease is short, LTFU is low, adequate funding

Question 7

When are retrospective studies used?

Answer 7

long follow up time required, temporality preserved

Question 8

when are cohort studies used

Answer 8

for rare exposures, multiple exposures for same disease, long follow up time btw exposure and disease, RCT is unethical, medium-long term follow up of drug performance

Question 9

What are the cons of cohort

Answer 9

high drop out rate, residual confounding, long wait for rare diseases, lil evidence to justify long study examining exposure-disease relationship, data quality might be poor, historical effect

Question 10

Define historical effect

Answer 10

advance in medicine may render old data obsolete for answering today’s questions

Question 11

Cohort participants are selected on

Answer 11

exposure

Question 12

Case participants are selected on

Answer 12

outcome

Question 13

Define selection bias

Answer 13

participants LTFU (drop out associated with outcome or unique exposure pattern)

Question 14

what are three examples of information biase?

Answer 14

observational/misclassfication bias, ascertainment bias, analytic bias

Question 15

define information bias

Answer 15

quality of info is diff btw groups

Question 16

define observational bias

Answer 16

quality and extent of info is diff btw exposed and unexposed

Question 17

define misclassification bias

Answer 17

quality and extent of info is diff btw exposed and unexposed

Question 18

define ascertainment bias

Answer 18

disease assessor knows exposure status

Question 19

define analytic bias

Answer 19

belief of investiggators influence data analysis and interpretation

Question 20

define relative risk

Answer 20

ratio of risk of disease in exposed to risk of disease in unexposed

Question 21

interpret relative risk

Answer 21

the risk of outcome in exposed is ___% higher/lower than risk of outcome in unexposed

Question 22

RR = 1

Answer 22

null value, risk in exposed = risk in unexposed

Question 23

RR>1

Answer 23

positive association

Question 24

RR<1

Answer 24

negative association

Question 25

When can OR approx RR?

Answer 25

when disease is rare

Question 26

When does ability of OR to estimate RR become worse

Answer 26

as disease prevalence increases

Question 27

Why cant we do RR for case control

Answer 27

bc we fix # of cases and controls

Question 28

What measure indicates the potential for prevention if exposure is eliminated?

Answer 28

attributable risk

Question 29

Equation for attributable risk?

Answer 29

incidence in exposed group - incidence in non-exposed group

Question 30

Attributable risk as proportion?

Answer 30

AR/ incidence in exposed group

Question 31

Incidence in total pop?

Answer 31

incidence in exposed*proportion of popEXPOSED + incidence in unexposed*proportion of popUNEXPOSED

Question 32

Population attributable risk?

Answer 32

incidence in total pop - incidence in unexposed group

Question 33

Population attributable risk %?

Answer 33

PAR/ incidence in total population

Question 34

Equation for incidence density?

Answer 34

of cases/# of PY

Question 35

Equation for incidence density ratio?

Answer 35

ID exposed/ ID unexposed

Question 36

Interpretation of ID ratio?

Answer 36

incidence of disease in exposed group is ___xx the incidence of disease in unexposed group

Question 37

What is a cross sectional study

Answer 37

identify exposure and disease status at same time and there is no follow up

Question 38

Cross sectional studies identify what

Answer 38

prevalent cases of disease in exposed and unexposed

Question 39

What are the pros of cross sectional studies

Answer 39

quick, cheap, useful for hypothesis generation, suggest need for CC or cohort

Question 40

What are the cons of cross sectional studies?

Answer 40

reverse causality bias, prevalent may not be representative of all cases

Question 41

Why doesnt RR apply to cross sectional studies?

Answer 41

bc subjects arent at risk or follows up

Question 42

What is causality bias

Answer 42

cant be sure exposure proceeded disease

Question 43

What is prevalence ratio

Answer 43

prevalence of disease in exposed/prevalence of disease in uexposed

Question 44

What is the interpretation of prevalence ratio

Answer 44

prevalence of disease in exposed is ____% higher/lower than prevalence of disease in unexposed

Question 45

What observational study does prevalence ratio apply to

Answer 45

cross sectional study