Question

researchers wanted to evaluate whether ginkgo, an over - the - counter herb marketed as enhancing memory, improves memory in elderly adults as measured by objective tests. to do this, they recruited 86 men and 130 women older than 50 years and in good health. participants were randomly assigned to receive ginkgo, 40 milligrams (mg) 3 times per day, or a matching placebo. the measure of memory improvement was determined by a standardized test of learning and memory. after 6 weeks of treatment, the data indicated that ginkgo did not increase performance on standard tests of learning, memory, attention, and concentration. these data suggest that, when taken following the manufacturers instructions, ginkgo provides no measurable increase in memory or related cognitive function to adults with healthy cognitive function. complete parts (a) through (g) below. (a) what type of experimental design is this? a. matched - pairs design b. randomized block design c. cohort study d. case - control study e. completely randomized design

Explanation:

In a completely - randomized design, subjects are randomly assigned to treatment groups. Here, participants are randomly assigned to receive ginkgo or a placebo without any matching or blocking. Matched - pairs design involves pairing similar subjects, randomized block design groups subjects into blocks first, cohort study follows a group over time, and case - control study compares cases and controls.

Answer:

E. Completely randomized design