QS20-21About Experiment Design

21] In an interesting experiment, researchers examined the effect of ultrasound on birth weight. Pregnant women participating in the study were randomly assigned to one of two groups. The rst group of women received an ultrasound; the second group did not. When the subjects' babies were born, their birth weights were recorded. The women who received the ultrasounds had heavier babies. 3] Did the experimental design take the placebo effect into account? Why is this important? b] Was the experiment double-blind? Why is this important? c] Based on your answers to a] and b], describe an improved design for this experiment 20) Twenty overweight females have agreed to participate in a study of the effectiveness of four weight- loss treatments: A, B, C, and D. The researcher first calculates how overweight each subject is by comparing the subject's actual weight with her "ideal" weight. The subjects and their excess weights in pounds are as follows: Birnbaum 35 Hernandez 25 Moses 25 Smith 29 Brown 34 Jackson 33 Nevesky 39 Stall 33 Bunk 30 Kendall 28 Obrach 30 Tran 35 Cruz 34 Loren 32 Rodriguez 30 Wilansky 42 Deng 24 Mann 28 Santiago 27 Williams 22 The response variable is the weight lost after 8 weeks of treatment. Previous studies have shown that the effects of a diet may vary based on a subject's initial weight. a) Explain why a randomized block design would be better than a completely randomized design in this setting. b) Should researchers form blocks of size 4 based on subjects' last names in alphabetical order or by how overweight the subjects are? Explain. c) Explain how you could carry out the random assignment required by your design. Explain your method clearly