lecture 5: cohort design

Question 1

what is the latin word for cohort mean

Answer 1

company or crowd

Question 1

what does the term cohort mean in every day language

Answer 1

Used in everyday language to describe a designated group of persons who are together over a period of time (e.g: university cohort

Question 2

true or false: cohorts are “population based” studies

Answer 2

true

Question 3

describe a population based study

Answer 3

Study subjects are collected from the entire population “at risk”
* Population is defined at the outset of study usually within
geographical or environmental boundaries
◦ e.g. individuals with myopia within McGill students, Island of Montreal,
province of Quebec, or continent of Africa

• Study sample often selected randomly
• Using proper sampling methods, study sample should be generally
  representative of population with respect to the distribution of pre pre-defined characteristics of interest
  (e.g. age, disease severity, income

Question 4

in a population based study, where are the study subjects collected

Answer 4

Study subjects are collected from the entire population “at risk”
*

Question 5

in population based study, how is the population defined

Answer 5

Population is defined at the outset of study usually within
geographical or environmental boundaries
◦ e.g. individuals with myopia within McGill students, Island of Montreal,
province of Quebec, or continent of Africa
*

Question 6

true or false: in population based design, the study sample is usually selected randomly and explain why

Answer 6

true because
* Using proper sampling methods, study sample should be generally
representative of population with respect to the distribution of pre pre-defined characteristics of interest
(e.g. age, disease severity, income

Question 7

what are the two types of sampling and explain

Answer 7

random:selecting sample randomly (every person in population has an equal prob of being selected

non random: ex: patients in your physio who aggree to be part of study (convenience sampling)

Question 8

what is the general design of a cohort study

Answer 8

looking for an assicaiton between exposure and outcome (like case control). you choose your population because on exposure and then follow them for a period of time to determine if they develop the outcome of interest

Question 9

what are the two types of cohort studies

Answer 9

prospective cohort
hisotical/restrospective cohort

Question 10

true or false: in a cohort, you choose your sample based on the outcome and look back to see their exposures

Answer 10

false, thats case control

in a cohort you choose your sample based on the exposure and then follow to measure outdone

Question 11

in cohort, you choose your sample based on exposure or outcome

Answer 11

exposure

Question 12

in case control, you choose your sample based on exposure or outcome

Answer 12

outcome

Question 13

true or false: cohort studies take place at one point in time

Answer 13

false, time is elapsing forward

Question 14

explain a prospective cohort study

Answer 14

researches choose a group of individuals based on their exposure status to something and Participants are followed forward in time,
The exposure status of participants is assessed at the beginning of the study, and they are then followed to observe the development of outcomes.
Prospective cohort studies are forward-looking and involve the collection of new data as the study progresses.

Question 15

explain historical cohort study

Answer 15

start by identifying a group of individuals who were exposed to a particular factor or condition in the past (before the study begins) look back at exists records or databases to identify individuals with the desired exposure status and then follow them forward in time to observe outcomes
=backward looking and rely on existsing data

Question 16

what is the advantage of using a retrospective cohortt instead of prospective

Answer 16

takes less time and money

Question 17

what is the main difference and main similarity between cohort and case control

Answer 17

you are looking at the relationship between exposure and outcome in both

in case control you start with the outcome and look retrospectively for the exposure levels

in cohort you are selecting based on exposure and you are moving forward to see the development of outcomes

Question 18

know the chart with observational designs

Question 19

where does a cross sectional design study fit in the research cycle

Answer 19

burden of disease

Question 20

where does a case control design study fit in the research cycle

Answer 20

mechanisms/assocaited

Question 21

where does a cohort design study fit in the research cycle

Answer 21

fits in the mechanisms/assocaitins

Question 22

what are the strengths of a cohort design

Answer 22

• Good for studying rare exposures and multiple outcomes
• Can establish temporal sequence, important in determining causality
• Can yield incidence
  (Cumulative incidence = # diagnosed / N)
  (Incidence density = # diagnosed / person person-years)
• Can yield different measures of association
  e.g. odds ratio, risk ratio, attributable risk, incidence ratio, hazard ratio

Question 23

what are the weakness/disadantages of cohort

Answer 23

very expensive
takes time to answer quetions
big commitment for partcipants

Question 24

what are the potential sources of bias in a cohort study

Answer 24

Losses to follow up (may lead to selection)

=Minimize bias during study by careful tracking, f/u of subjects, incentives
=In analysis, compare characteristics between those lost to f/u and those remaining in study sample
*
Knowledge of exposure may influence disease or outcome
classification by evaluators
(information)
=Minimize by blinding evaluators to exposure status and to study
hypothesis

Question 25

explain how to minimize selection bias in cohort

Answer 25

=Minimize bias during study by careful tracking, f/u of subjects, incentives
=In analysis, compare characteristics between those lost to f/u and those remaining in study sample

Question 26

explain how to minimize infromation bias in cohort

Answer 26

=Minimize by blinding evaluators to exposure status and to study
hypothesis