Lecture 16

Question 1

cohort study designs basic

Answer 1

participants are chosen from a population that is AT RISK of developing outcome of interest
- participants are classified as exposed or unexposed
- - exposure is observed not assigned
- follow participants forward in time

Question 2

population type (source v sample)

Answer 2

source - group of people which the study participants will be selected (Duquesne students)

sample - the people what are actually selected for the source population (students in epidemiology)

Question 3

developing a hypothesis

Answer 3

PICO question
- investigators may want to learn about many things that are in a broad research area
- cohort studies are designed to study one or many hypotheses

Question 4

steps in a cohort study

Answer 4

1. state the research question
   - objective and hypothesis
2. design the trial
   - define exposures / outcomes
   - define cohort
3. conduct the trial
   - selection of subjects
   - follow and collect data
4. analyze and report the data

Question 5

cohort

Answer 5

a well -defined group of individuals who are at risk for the outcome of interest at the start of the follow-up period and are followed or traced over a period of time

Question 6

birth cohort

Answer 6

a cohort defined by being born during a particular period of time

Question 7

general population cohort

Answer 7

used if the goal of the cohort is to value the effects of exposures which commonly occur in large populations
- broad admission criteria
- investigators can assess a wide range of exposures and outcomes

Question 8

special exposure

Answer 8

participants are intentionally selected on the basis of their exposure status
- good for rare exposures

Question 9

closed cohorts

Answer 9

defined by a common start time, and no on his added to the cohort during the follow up period
- only exit the cohort If they get the outcome of interest, study ends or they die
- it is difficult to maintain
- analyzed by RISK

Question 10

open (dynamic) cohort

Answer 10

allow members to enroll and leave at different times
- person-tine contributed by individuals vary
- analyzed by RATE

Question 11

real time (prospective) cohorts

Answer 11

occurs when investigators identify and enroll a cohort of at-risk individuals and follow them forward in real time to see who develops outcome of interest
- pro: recruitment and data collection are controlled by investigators
- con: more expensive, latency period

Question 12

historical (retrospective) cohorts

Answer 12

use historical records to understand what has happened to a cohort of individuals in the past
- pro: cheaper, faster
- con: must relay on exiting data which cannot change how it was collected

Question 13

exposure groups

Answer 13

• should be as similar as possible to reference group
• confounders: any extraneous factors that may be associated with the outcome of interest

Question 14

internal reference group

Answer 14

comprised of the unexposed members of the cohort
- used in general population cohorts

Question 15

external reference group

Answer 15

comprised of unexposed individuals from some external group
- used in special exposure cohorts. since everyone has special exposure, your reference has to come from an outside group

Question 16

risk period

Answer 16

time during which an exposure of interest could possibly cause an outcome
- includes induction and latency period

Question 17

induction period

Answer 17

time it takes for an outcome to occur due to an exposure of interest

Question 18

latency period

Answer 18

time during which an outcome exists but is not clinically or otherwise diagnostically detectible

Question 19

induction and latency period

Answer 19

are important when calculating measures of incidence because they help define who is at risk of developing the outcome DUE to the exposure of interest

Question 20

incubation period

Answer 20

reserved for infectious diseases and is defined as the time between when exposure to an infectious agent occurs and symptoms begin

Question 21

strengths of cohort studies

Answer 21

1. temporality
   - given that the exposure status is observed and/or recorded prior to the occurrence of the outcome, the temporality between exposure and outcome is established by cohort design
2. study of rare exposures
   - relatively well suited for study rare exposes or exposures that would occur infrequently int eh general population
3. study of several outcomes
   - allow study of associations between multiple exposures on several outcomes allowing researchers to test multiple hypotheses
4. calculation of measures of outcome frequency
   - allows investigators to calculate the risk or rate of the health outcome under study (researchers better understand changes in outcome frequency over time)

Question 22

limitations in cohort studies

Answer 22

1. loss to follow up
   - can lead to selection bias
2. study of rare outcomes
   - investigators may not observe enough people with outcomes to detect difference in their occurrence between exposure groups
3. study of exposure outcomes relationship with long induction period of outcomes with long latency periods
   - investigators would have to wait a long time to collect data and draw conclusions
4. logistics
   - can be expensive, time consuming and resource intensive