lecture 5: cohort design Flashcards
what is the latin word for cohort mean
company or crowd
what does the term cohort mean in every day language
Used in everyday language to describe a designated group of persons who are together over a period of time (e.g: university cohort
true or false: cohorts are “population based” studies
true
describe a population based study
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
in a population based study, where are the study subjects collected
Study subjects are collected from the entire population “at risk”
*
in population based study, how is the population defined
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
*
true or false: in population based design, the study sample is usually selected randomly and explain why
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
what are the two types of sampling and explain
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)
what is the general design of a cohort study
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
what are the two types of cohort studies
prospective cohort
hisotical/restrospective cohort
true or false: in a cohort, you choose your sample based on the outcome and look back to see their exposures
false, thats case control
in a cohort you choose your sample based on the exposure and then follow to measure outdone
in cohort, you choose your sample based on exposure or outcome
exposure
in case control, you choose your sample based on exposure or outcome
outcome
true or false: cohort studies take place at one point in time
false, time is elapsing forward
explain a prospective cohort study
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.
explain historical cohort study
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
what is the advantage of using a retrospective cohortt instead of prospective
takes less time and money
what is the main difference and main similarity between cohort and case control
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
know the chart with observational designs
where does a cross sectional design study fit in the research cycle
burden of disease
where does a case control design study fit in the research cycle
mechanisms/assocaited
where does a cohort design study fit in the research cycle
fits in the mechanisms/assocaitins
what are the strengths of a cohort design
- 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
what are the weakness/disadantages of cohort
very expensive
takes time to answer quetions
big commitment for partcipants
what are the potential sources of bias in a cohort study
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
explain how to minimize selection bias in cohort
=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
explain how to minimize infromation bias in cohort
=Minimize by blinding evaluators to exposure status and to study
hypothesis
