Choose the study design that best matches each statement described below. The study design may be used more than once or none at all. (24 points) Statement
Study Design
Blinding or masking is used to control potential bias.

Case-Control
Observational epidemiological studies, this design is cheaper and faster to conduct because of the usage of already existing data.
Cross-sectional
Control groups can receive the current "standard" treatment or a placebo.
Ecological
Data on exposure and outcome at the individual level is gathered at one point in time.
Prospective Cohort
Disease-free individuals are enrolled based on a defined population or exposure at the present then followed up over time to see who develops the disease of interest.
Retrospective Cohort
Efficient for multiple exposures.
Randomized Clinical Trial
Efficient for multiple outcomes.
Efficient for rare outcomes.
For each case recruited into the study, a sex- and age-matched control was recruited.
Observational study with greater potential for loss-to-follow up.
Have the highest internal validity.
Inexpensive study that can be quickly conducted when individual level data are not available.
Less expensive design useful for diseases that are prevalent and of long duration.
Preferred when the variability of exposure within the group is low or variability of exposure between groups is high.
Randomization after enrollment confirms that participants have an equal probability of being in the exposed or unexposed groups.
Subjects with and without the outcome of interest are enrolled and then evaluated if they had a history of exposure in the past.