Cohort Studies

Question 1

Descriptive studies

Answer 1

Describe a disease condition (signs, lesions, outcomes, etc)

• case reports, case series, surveys
• no hypothesis, controls, cannot evaluate effect of treatments
• does not offer proof that risk factor causes disease
• goal: to compare findings

Question 2

Explanatory studes

Answer 2

Seek to identify causes

• has hypothesis and controls
• investigates a treatment, intervention, risk factor in hopes of providing causal evidence

Question 3

Experimental studies

Answer 3

Element of randomization

• experimenter assigns animal to a treatment (researcher has greatest control)
• does not represent real world conditions
• lab studies, clinical trials

Question 4

Observational

Answer 4

Epidemiologic

• cohort
• case control
• cross sectional

Question 5

Which study is best to prove cause or demonstrate efficacy?

Answer 5

Experimental - laboratory

Question 6

Clinical trials

Answer 6

Assess efficacy of a preventative or therapeutic treatment or intervention

• planned comparison between 2 groups
• animals maintained under field conditions
• disease is naturally occurring
• researcher has less control over animals/housing/challenge than in lab experimental trial

Question 7

Which study has findings that are more generalizable to field conditions?

Answer 7

Experimental study with clinical trials

Question 8

Which study is also called “natural studies”

Answer 8

Observational (epidemiologic) studies

• occur freely in nature
• similar to explanatory (goal is to assess the cause)
• controls and planned comparisons between groups
• do not provide sufficient evidence to establish cause

Question 9

What is the difference between observational and explanatory studies?

Answer 9

In observational studies the allocation of animals to treatment groups is not under control of the researcher

Question 10

Cohort study

Answer 10

Prospective in time

• feature 2 cohorts: one exposed to a factor and one not exposed to that factor
• subjects followed in time, incidence of 1 or more diseases are compared between 2 cohorts

Question 11

What is the primary measure of a cohort study?

Answer 11

Simple cumulative incidence

Question 12

2 x 2 table

Answer 12

• exposure status in left column
• disease (outcome) in top row
• positives go together

Question 13

What are 3 questions to ask in a cohort study that can be answered using the 2 x 2 table?

Answer 13

• what is the proportion of exposed that develop the disease
• what is proportion of unexposed that develop disease
• how do these compare

Question 14

Are you looking at incidence or prevalence with a cohort study?

Answer 14

Incidence

Question 15

When you are looking at how the 2 cohorts compare, you are measuring _______

Answer 15

Relative risk of disease in exposed, compared to unexposed

- risk of disease in exposed is _____ times higher than risk of disease in unexposed

Question 16

Disease vs factor table

Answer 16

Look at powerpoint and memorize!!

Question 17

Relative risk formula

Answer 17

a/(a+b) / c/(c+d)

Question 18

A cohort study is good for diseases that are relatively ______

Answer 18

Common

- cannot compute a relative risk if the disease occurrence is zero

Question 19

The measure of association for a cohort study is ______

Answer 19

Relative risk

Question 20

Relative risk > 1 indicates

Answer 20

Increased risk in exposed, compared to unexposed

Question 21

Relative risk = 1 indicates

Answer 21

Risk in exposed is the same as in unexposed

Question 22

Relative risk < 1 indicates

Answer 22

Disease in exposed is less than in unexposed

- exposure has a sparing effect, or a reduction in risk associated with exposure

Question 23

A relative risk is the measure of the ________ between a factor and a disease

Answer 23

Strength of association

• compares probability of disease in a population with the factor/exposure to the probability of disease in a population without the factor/exposure
• can only be estimated in a cohort, cross-sectional, or experimental study

Question 24

Can relative risk be estimated in a case-control study?

Answer 24

No

Question 25

Relative risk is proportion ______

Answer 25

with disease in exposed/proportion with disease in unexposed

Question 26

In a cohort study, is the time sequence of “cause” and disease clear?

Answer 26

Yes

• animals are disease free at the beginning
• exposure documented to occur before disease

Question 27

Observational studies are well suited to study the effect of ________

Answer 27

Multiple outcomes following a single exposure

- exposure to a single toxin: acute disease, neoplasia, in utero effects

Question 28

Factor A causes disease X if _______

Answer 28

• factor A occurs before disease X (temporal relationship)

- factor A is present very often in cases, and not in controls (strength of association)

Question 29

The more _____ you have, the greater the disease chance

Answer 29

Factor A

• dose response relationship
• stratify severity over conditioning

Question 30

Biological plausibility

Answer 30

Based on what is known, factor A could cause disease X

Question 31

Consistency of multiple studies

Answer 31

Relationship between factor A and disease X is seen repeatedly, time and time again

Question 32

Reversible associations

Answer 32

Removal of factor A results in diminished disease

Question 33

What does risk of disease in unexposed represent?

Answer 33

Control/base line