09. Cohort & Case-Control

Question 1

Types of observational studies

Answer 1

COHORT; CASE-CONTROL; Ecological (aggregate-level); Cross-sectional (snapshot)

Question 2

Observational studies

Answer 2

Nothing is manipulated; researcher classifies people as those already exposed vs. not exposed

Question 3

Types of experimental studies

Answer 3

RCT; Preventive trials; Community trials

Question 4

Defining characteristic of an experimental study

Answer 4

Researcher assigns protocol or manipulates exposure

Question 5

Individual/Personal-level data

Answer 5

Individuals are classified according to a trait and incidence of disease is compared between groups

Question 6

Aggregate-level (ecological) data

Answer 6

Regional data is compared; individual scores are not used directly

Question 7

Longitudinal observations

Answer 7

Individuals are observed OVER TIME to compare disease incidence

Question 8

Cross-sectional observations

Answer 8

Population is RANDOMLY SAMPLED and individuals are classified into groups and POINT PREVALENCE is compared in the classifications (snapshot)

Question 9

Cohort study

Answer 9

Group of individuals having a statistical factor in common. Subjects are selected based on exposure; best observational method available. All subjects at beginning of study are disease free, disease susceptible, and observed over a meaningful period of time. PROGNOSIS is best studied with a cohort. Cohorts are also useful for etiology and prevention.

Question 10

Prospective cohort

Answer 10

Observational study where investigator starts the follow-upand waits for the outcome (event of interest) to occur. May take years and are difficult to conduct.

Question 11

Retrospective cohort

Answer 11

Outcomes (events of interest) have already happened at some point in the past; investigator simply goes back even further and selects exposed and unexposed people. Easier to perform than prospective cohort studies but researcher has less control over data quality and reliability.

Question 12

Case-control studies

Answer 12

Subjects are selected based on disease; 2nd best observational study; compares odds. USED FOR RARE DISEASES, BUT WE CAN’T MEASURE RELATIVE RISK.

Question 13

Advantages of cohort studies

Answer 13

Only direct means to establish absolute risk; Unbiased measure of exposure; Can assess relationship between single exposure and MANY diseases

Question 14

Disadvantages of cohort studies

Answer 14

Impractical for rare diseases; Costly in terms of money and time; Can only assess one exposure

Question 15

Odds ratio definition

Answer 15

The odds that an outcome will occur given a particular exposure, compared to the odds of the outcome occurring in the absence of exposure. [Odds of exposure in disease/Odds of exposure in non-disease] = [AD/BC] = OR

Question 16

Use of Odds Ratio

Answer 16

Used in case-control studies to determine odds of developing a disease due to a particular exposure; approximates risk ratio in rare disease. However, it OVERESTIMATES RR in COMMON disease.

Question 17

Risk ratio definition

Answer 17

Proportion of the original risk that is still present when patients receive the experimental treatment; {[A/(A+B)] / [C/(C+D)]}

Question 18

Use of Risk Ratio

Answer 18

used in COHORT studies, NOT in CASE-CONTROL.

Question 19

Possible Study Types for Therapy Questions

Answer 19

RCT

Question 20

Possible Study Types for Diagnosis Questions

Answer 20

RCT

Question 21

Possible Study Types for Prognosis Questions

Answer 21

COHORT (BEST!); Case-Control; Case Series

Question 22

Possible Study Types for Etiology Questions

Answer 22

Cohort; Case-Control

Question 23

Possible Study Types for Prevention Questions

Answer 23

RCT; Cohort

Question 24

Possible Study Types for Quality Improvement Questions

Answer 24

RCT

Question 25

What types of questions can be evaluated with a cohort study?

Answer 25

PROGNOSIS (best); etiology; prevention. NOT THERAPY

Question 26

What types of questions can be evaluated with a case-control study?

Answer 26

Prognosis (2nd to cohort); etiology

Question 27

What types of questions can be evaluated with a RCT?

Answer 27

Therapy; diagnosis; Prevention; Quality improvement