BIOL 437 Week Eight P.3 (Statistical Methods in Analytical Epidemiology)

Question 1

double cohort

Answer 1

• 2 distinct populations are invovled with different levels of an exposure of interest
• employed when expsoure is rare and a relatively small number of people are affected

Question 2

selecting the study cohort

Answer 2

-from population

>chose those at risk of becoming a case

Question 3

exclude from study cohort

Answer 3

• those who already have a disease outcome of interest
• those not at risk
• those with latent infections or recurring diseases

Question 4

restriction

Answer 4

• used to improve validity of study
• selecting cohorts with limited exposure, narrow behaviours
• need to come from population where sampling can be effectively conducted
• limits generalization, but often improves feasibility and focus

Question 5

bias in cohort studies

Answer 5

1. Selection bias
2. Confounding
   >more a concern in double cohort studies
3. Misclassification

Question 6

selection bias types

Answer 6

1. Healthy worker effect
2. Volunteer bias
3. Loss to follow-up

Question 7

healthy worker effect

Answer 7

• when workers represent exposed group and sample from general population represents the unexposed
• workers tend to be healthier on average than the general population

Question 8

loss to follow-up

Answer 8

• lose contact, resulting in unavailable outcome data
• common problem
• general rule: validity of study requires a loss of follow-up not exceeding 20%

Question 9

reasons for loss to follow-up

Answer 9

• refusal to participate
• unable to locate
• unable to be interviewed
• death

Question 10

confounding

Answer 10

• more a problem in double-cohort studies

- can influence associates in both case-control and cohort studies

Question 11

differential misclassification

Answer 11

• related to exposure
• if exposure classification influences differential accuracy in ascertaining outcome info
• overestimates association

Question 12

non-differential misclassification

Answer 12

-not related to exposure
-through inaccuracies in classifying exposure status
>occur similarly between exposed and unexposed
-underestimates association
-error affects both groups and can make them more similar

Question 13

avoid healthy worker bias

Answer 13

-selecting a comparison group made up of workers, only unexposed

Question 14

minimize misclassification

Answer 14

• refine definition of exposed and unexposed

- avoid exposure classifications that result in differential outcome ascertainment

Question 15

minimize loss to follow-up bias

Answer 15

• restrict study to those likely to remain
• collect personal identifying info
• make periodic contact and provide incentives

Question 16

control confounding at study design level

Answer 16

-restriction to avoid bias due to confounding
-in double cohort:
>choose comparisions as a like as possible to the exposed population

Question 17

control confounding at analysis level

Answer 17

-collect data on potential confounders at begining

>adjust through stratification and multiple regression techniques

Question 18

effect modification

Answer 18

• when association between exposure and outcome is modified by the level of an extrinsic factor beyond random variation
• may occur in cohort or case-cohort

Question 19

effect modifier

Answer 19

-extrinsic variable

Question 20

effect modification can influence

Answer 20

-relationship between variables in cohort and case-control data
>can influence OR, RR, and rate ratios

Question 21

confounding vs. effect modification

Answer 21

• treated differently
• control for confounding
• present results from effect modificaiton
• sometimes a variable can act as a confounder and an effect modifier

Question 22

effect-modifying variable

Answer 22

• influences association between 2 other variables in an informative way
• can be informative and meaningful

Question 23

if OR crude > OR1=OR2

Answer 23

-positive confounding

Question 24

if OR crude < OR1=OR2

Answer 24

-negative confounding

Question 25

OR1=OR2

Answer 25

-effect modification present