1.3 observational studies Flashcards
experimental units
individuals who are studied (i.e. people, animals, plants, plots of land or things) people are sometimes called subjects
treatment
procedures applied to each experimental unit (i.e. type of seed, formaldehyde level)
outcome/response
what is measured on each experimental unit (i.e. amount of growth, degree of respiratory problems)
randomized experiment
study in which the investigator assigns treatments to the experimental units at random
observational study
one in which the assignment to treatment groups is not made by the investigator
why randomize?
in reality, treatment groups differ from each other no matter how much they are alike.
randomization makes small differences only due to chance
large differences in outcomes among groups can be concluded that the differences are due to the treatments
why observational studies are less reliable AKA confounding?
it’s hard to tell whether a difference in the outcome is due to the treatment or to some other difference between the treatment and control groups. AKA confounding
what are the two types of observational studies?
cohort and case-control
what are the types of cohort studies?
prospective, cross-sectional, retrospective
cohort study
group of subjects is studied to determine whether carious factors of interest are associated with an outcome
prospective cohort study
where the subjects are followed over time
cross-sectional
where measurements are taken at one point in time (i.e. when the respiratory problems were measured on one point a time in a single day)
retrospective cohort study
subjects are sampled after the outcome has occurred
case-control study
two samples are drawn. there are the cases and the controls. the investigators look back in time to determine whether a factor of interest differs between the two groups
the cases
the people of have the disease of interest
