BIOL 437 Week Eight P.2 (Statistical Methods in Analytical Epidemiology)

Question 1

misclassification

Answer 1

• occurs when either the exposure or the outcome status is inaccurately assigned
• most case-control studies have some level of it

Question 2

types of misclassification

Answer 2

1. Differential (non-random)

2. Non-differential (random)

Question 3

differential (non-random)

Answer 3

• classification of history is accurate in 90% of of cases and 100% of controls
• level of misclassification is different
• results in under or over estimation of OR

Question 4

non-differential (random)

Answer 4

• classification of history is accurate in 90% of cases and 90% of controls
• level of misclassification is the same
• results in understimating OR

Question 5

confounding

Answer 5

-occurs when an extrinsic factor is associated with a disease outcome
-independant of that association, it is also associated with the exposure
Ex. coffee consumption, smoking and myocardial infraction

Question 6

matching

Answer 6

• a strategy for controlling confounding at both the design and analysis levels of a study
• distribution of potential confounding factors is forced to be similar betweeen cases and controls

Question 7

case-crossover study design

Answer 7

• compares exposure status of a case immediately before its occurennce with that of the same case at a prior time
• each case as their own control

Question 8

case-crossover study appropriate when

Answer 8

• individual exposures are intermittent
• disease occurs abruptly
• incubation period for detection
• induction period are short

Question 9

analytic unit for case-crossover

Answer 9

• time

- just before the acute event is the ‘case’ time, compared with some other time: ‘control’ times

Question 10

nested case-control study design

Answer 10

• case-cohort study
• case-control study “nested” within a cohort study
• sample of cases and controls are selected and exposure status compared

Question 11

cohort studies

Answer 11

• a group of persons being studied who were born in the same year or period
• generally involves study of persons who have been exposed and are followed over time
• can be prospectively (forward in time) or retrospectively (backward in time)

Question 12

prospective cohort study

Answer 12

-predictor variable is measured before to outcome has occured

Question 13

retrospective cohort study

Answer 13

-a historical cohort is reconstructed with data on the predictor variable and data on the outcome collected

Question 14

cohort effect

Answer 14

• generation effect
• change in disease or health status of a study population as they move through time
• includes any exposure or influence, from environmental effets to societal changes

Question 15

advantage of cohort over case-control

Answer 15

-incidence rate of several outcome variables can be determined and associated with the exposure variable

Question 16

common measures for describing cohort data

Answer 16

1. Cumulative incidence rate: attack rate

2. Incidence density rate: person-time rate

Question 17

measures of association in cohort studies

Answer 17

1. Ratio of attack rates

2. Ratio of person-time rates

Question 18

ratio of attack rates

Answer 18

• risk ratio (relative risk) (RR)

- probability of health event among those exposed relative to those unexposed

Question 19

ratio of person-time rates

Answer 19

• rate ratio
• cumulative incidence rate of disease among exposed relative to unexposed
• only able to calculate when total time the exposed and unexposed are at risk is known

Question 20

person-time

Answer 20

• for acute: hours, days, weeks, sometimes months

- for chronic: years

Question 21

RRs as %

Answer 21

• RR>1: % increase change (RR-1)x100

- RR<1: % decrease change (1-RR)x100

Question 22

attributable risk (AR)

Answer 22

• cumulate incidence in exposed group minus unexposed

- difference in attack rates or in person-time rates

Question 23

attributable risk intrepreted as

Answer 23

• excessive risk of disease among the exposed group attributed to the exposure
• absolute risk in exposed group that is attributable to the exposure

Question 24

AR% intrepretation

Answer 24

-certain % of disease in group is attributed to the exposure

Question 25

population attributable risk (PAR) intrepretation

Answer 25

• if exposure was eliminated, the amount the rate would drop
• assumes casual association between exposure and disease

Question 26

PAR equals

Answer 26

-person-time rate in total population minus person time-rate in unexposed population

Question 27

PAR % intrepretation

Answer 27

-the % decrease if the exposure was eliminated