cohort studies

Question 1

what are cohort studies

Answer 1

starting point -> exposure to the outcome of interest
exposure status defined before outcome is assessed - temporality

Question 2

how to calculate the risk of outcome for those exposed and those unexposed

Answer 2

incident risk in exposed = a/ a+b
interpretation: the probability of developing the outcome in everyone exposed was … %

incident risk in unexposed= c/ c+d
interpretation: the probability of developing outcome in everyone not exposed was …%

Question 3

how to compare/contrast the “risk” across exposure groups

Answer 3

relative risk or risk ratio (RR)
risk difference (RD)

Question 4

what is relative risk (risk ratio)

Answer 4

assess strength of association- compares incidence of disease between those exposed and unexposed

risk in unexposed

interpretation: risk of developing lung cancer is 15.6 times higher for those who smoke compared to those who did not

Question 5

what is risk difference

Answer 5

measures clinical and public health importance of the casual relationship

risk in exposed - risk in unexposed

interpretation: the excess risk of lung cancer due to smoking is …%

Question 6

what does an increased vs decreased risk ratio mean

Answer 6

RR > 1 = exposure is harmful
RR < 1 = exposure is protective
RR = 1 = exposure does nothing

Question 7

how to translate RR to a precent relative effect

Answer 7

if RR > 1% increase = (RR -1) x100
if RR < 1% decrease = (1-RR)x 100

Question 8

what is person-years

Answer 8

total number of years the study subjects have contributed

Question 9

how to calculate a rate (incidence rate)

Answer 9

persons-years

Question 10

what can we measure from cohort studies

Answer 10

incidence: risk and rate
effect: RR and risk difference

Question 11

different types of cohort studies

Answer 11

prospective
retrospective

Question 12

why do we need cohort studies

Answer 12

infrequent/ unusual outcomes related to infrequent exposure
temporal sequence needs to be established
interested in risk over time

Question 13

assumptions of a cohort study

Answer 13

participants are identical in all aspects but exposure
- especially prone to confounding factors

Question 14

advantages of cohort study

Answer 14

temporality -> exposure precedes outcome since cohort is disease-free at baseline
no recall bias
can study multiple outcomes associated with rare exposures
it is possible to estimate all measures of incidence (risk, rate) and effect (risk difference and risk ratio)

Question 15

disadvantages of a cohort study

Answer 15

requires large