POPH192- Lecture 19

Question 1

what type of study is cohort study?

Answer 1

analytic and observational

Question 2

what is the first step of cohort study?

Answer 2

1. identify a source population

Question 3

what is the second step in a cohort study?

Answer 3

2. recruit the sample population who don’t have the outcome of interest

Question 4

what is the third step in a cohort study?

Answer 4

assess their exposure level and categorise participant into appropriate group

Question 5

what is the fourth step in cohort study?

Answer 5

follow up overtime and see who develops the outcome

Question 6

what is the fifth step in cohort study?

Answer 6

calculate your measures of associations and occurrence

Question 7

what do we know in cohort studies that we don’t know in cross-sectional or ecological study?

Answer 7

• that the exposure came before the outcome

Question 8

how are individuals defined in cohort studies?

Answer 8

on the basis of presence or absence of exposure to a suspected risk factor

Question 9

what calculations are used in cohort studies?

Answer 9

• incidence proportion
• incidence rate
• relative risk
• relative difference

Question 10

what are some important things to consider in a cohort study? (5)

Answer 10

• the healthy worker effect
• need to be sure that the sample population doesn’t have the outcome
• need to ensure participants have been correctly classified into exposure groups
• loss to follow up (did any participants leave the study?)
• has the outcome been correctly classified?

Question 11

what is the healthy worker effect?

Answer 11

• when studies are derived only from a population of adult workers, this cannot be generalised to he population at large.
• this is because those who are working are overall healthier than those who are not

Question 12

what are the strengths of a cohort study?

Answer 12

• temporal sequence between exposure and outcome
• can look at multiple outcomes
• can calculate incidence, relative risk and risk difference
• good for rare exposures

Question 13

what are the limitations of cohort study?

Answer 13

• loss to follow up and it’s associated bias
• potential for exposure/outcome misclassification
• time consuming
• expensive
• not good for rare outcomes

Question 14

what are the two types of cohort studies?

Answer 14

• prospective
• historical

Question 15

what is a prospective cohort study?

Answer 15

• starting when everyone is outcome free and following them up

Question 16

what is historical cohort study?

Answer 16

start with outcome and use existing data to reconstruct the follow up (goes back in time)

Question 17

what are most cohort studies?

Answer 17

prospective

Question 18

what are historical cohort studies good for?

Answer 18

good for outcomes which are rare or take a long time to develop, are less expensive and less time consuming

Question 19

what may cause problems in historical cohort studies?

Answer 19

• data quality
• selection bias
• incomplete information

Question 20

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

Answer 20

in a case control, the investigator splits individuals by disease status whereas in retrospective (historical) cohort, the investigators splits individuals by their exposure status