Level IIa Evidence

Subjects who rely on AAC / Group Research

·Non-randomized controlled trial
·Prospective cohort study with concurrent control group

Prospective research involves the examination of variables through direct recording in the present. Prospective studies are more reliable than retrospective studies because of the potential for greater control of data collection methods.

Cohort study
A cohort is defined as a group of individuals who are followed together over time. In a cohort study (also called a follow-up study), the researcher selects a group of subjects who do not yet have the outcome of interest and follows them to see if they develop the disorder. Subjects are interviewed or observed on a periodic basis to determine the extent of certain exposures. Cohort studies may be purely descriptive, with the intent of describing the natural history of a disease. More often, however, they are analytic, identifying the risk associated with these exposures by comparing the incidence of specific outcomes in those who were and were not exposed (Portney & Watkins, 281).

Reference
Portney, L. G., & Watkins, M. P. (1993). Foundations of clinical Research: Applications to practice. Norwalk, CT:Appleton & Lange.