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Terms in this set (35)
a group of similar people followed through time together
follows participants through time to calculate the rate at which new (incident) disease occurs and to identify risk factors for the disease
all cohort studies have at least _ _________
2 measurement times
-an initial survey that determines the baseline exposure and disease status of all participants
-one or more follow up assessments that determine how many participants have developed a new (incident) disease since the initial examination
retrospective & prospective cohort study
recruit participants based on their exposure status
-one group of participants is recruited because they are known to have had a particular exposure
-a second group is recruited because they are known not to have been exposed
use baseline information collected at some point in the past and follow the cohort to another point in the past or to the present
collect baseline data about exposures and outcomes in the present and follow the cohort at some point in the future
_______ makes retrospective and prospective cohort studies the optimal study approaches for uncommon exposures
recruiting based on the exposure status makes retrospective and prospective cohort studies the optimal study approaches for uncommon exposures
because the goal of cohort studies is to examine incident disease, retrospective and prospective studies must be able to demonstrate...
because the goal of cohort studies is to examine incident disease, retrospective and prospective studies must be able to demonstrate that the outcome of interest was not present in any members of the cohort at baseline
the members of the 2 comparison groups for both retrospective and prospective of studies should be similar except for their _____
-recruit industrial workers exposed to a certain chemical and similar workers in a plant that does not use chemical
-recruit children with high blood lead levels (indicating environmental exposure to lead) and low blood lead levels who attend the same school
recruit participants based on their membership in a well-defined source population, then follow them forward in time
-individual participants are assessed at baseline for several exposures and diseases
-then they are followed forward in time to determine the incidence rate for one or more outcomes of interest
examples of populations for longitudinal studies
-all the residents of one town
-a representative sample of members of one professional organization
-a representative group of students recruited from the same university
all participants start the study at the same time and no one is allowed to join later
participants are recruited using rolling admission and replacement of dropouts
-the time to follow up is usually based on individual participants' dates of enrollment rather than on a fixed calendar date
loss of participants to follow-up before the end of the study period is a major concern
-researchers must develop strategies that minimize the burden of participation and that maximize interest in continuing to participate
all participants must complete the same assessments of exposure and disease at baseline and follow-up to prevent the info bias that might result when exposure participants are more thoroughly examined for disease than unexposed participants
# of new cases of disease in a population during a specified period of time divided by the total number of persons in the population who were at risk during that period
people who got it/people who could have got it (at risk)
-individuals who already have the disease of interest at the start of the study period aren't at risk of getting new disease, so they are removed from the denominator
a way of accounting for different individuals in the study population being observed for different lengths of time
-example: over 4 years in a dynamic study, 10 participants may contribute 33 person-years of observation
attributable risk (AR) or excess risk
the absolute difference in the incidence rate between the exposed population and the unexposed population
- if 10% of the unexposed and 15% of the exposed became ill during the study period, then the excess risk in the exposed was 15%-10%=5%.
-this number represents the additional risk of disease in the exposed that can be attributed to the exposure
the proportion of incident cases among the exposed that are due to the exposure
-if 10% of the unexposed and 15% of the exposed became ill during the study period, then the AR% is 5%+15%=33%
-1/3 of the cases of disease in the exposed could have been prevented if the exposure was removed
rate ratio (RR)
ratio of incidence rate among the exposed to the incidence rate in the unexposed
incidence rate in exposed: exposed w disease/(exposed w disease + exposed w no disease)
the incidence rate was the same in the exposed and in the unexposed, so the exposure is not associated with the disease
then the incidence rate was higher in the exposed than in the unexposed, so the exposed was risk factor
the incidence rate was lower in the exposed than in the unexposed, so the exposure was protective factor
if 95% CI<1, then RR...
then RR is statistically significant, and the exposure is protective factor in the study population
if 95% CI>1 then RR...
is statistically significant, and the exposure is a risk factor for disease in the study population
if 95% CI=1 then RR
is not statistically significant, and the exposure and disease are deemed to have no association
prospective or retrospective cohort primary study ?
is exposure associated with an increased incidence of disease?
prospective or retrospective cohort population
participants must be similar except for exposure status
-because the goal is to look for incident disease, no one can have the disease of interest at the start of the study
when to use prospective or retrospective cohort
an exposure is relatively uncommon, but a source of exposed individuals is available
prospective or retrospective cohort requirements
a source of individuals with the exposure is available
longitudinal cohort study primary ?
is exposure associated with an increased incidence of disease?
longitudinal cohort study population
participants must be available for follow-up months or years after enrollment
-study population must be reasonably representative of the population from which they were drawn
when to use longitudinal cohort study
the goal is to examine multiple exposure and multiple outcomes, and time is not a concern
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