Stat 245 Recitation 6 10/9/07 TA: Dongmei Li

10/9/ Recitation TA: Dongmei Li Announcement Homework 2 grades and solutions have been posted on Carmen website. Homework 3 (consists of problems 2.46, 2.48, 2.50, 2.60, 2.64, and 2.66 ) is due Wednesday (Oct. 10) in Lecture or in drop box on 122 Cockins Hall by 2:00pm Wednesday.

10/9/ Recitation TA: Dongmei Li Use of a Placebo Placebo is something that is identical (in appearance, taste, feel, etc.) to the treatment received by the treatment group, except that it contains no active ingredients. Why we use placebo in our experiments? In experiments using human subjects, use of control group may not be enough to determine whether a treatment does have an effect. People sometimes respond merely to the power of suggestion!!!

10/9/ Recitation TA: Dongmei Li An Example Suppose a study designed to determine whether a particular herbal supplement is effective in promoting weight loss uses an experimental group that takes the herbal supplement and a control group that takes nothing. What could happen? It is possible that those who take the herbal supplement and believe that they are taking something that will help them to lose weight may be more motivated and may unconsciously change their eating behavior or activity level, resulting in weight loss!

10/9/ Recitation TA: Dongmei Li Some Question Response variable? Weight Loss Quantitative or numerical Continuous Explanatory variable? Treatment (taking herb supplement or placebo) Categorical

10/9/ Recitation TA: Dongmei Li Using a placebo in control group Individual in control group take placebo instead of nothing will respond to the treatment in similar ways as long as they do not know whether they are taking the herb or placebo. The placebo group would provide a better basis for comparison and would allow the researchers to determine whether the herbal supplement had any real effect over and above the “placebo effect.”

10/9/ Recitation TA: Dongmei Li Single-blind & Double-blind Single-blind  An experiment in which subject do not know what treatment they have received is described as single-blind. Double-blind  If participants do not know what treatment was received and those measuring the response do not know which treatment was given to which participant, the experiment is described as double-blind.

10/9/ Recitation TA: Dongmei Li 2.49 on page 55 Researchers at the University of Pennsylvania suggest that a nasal spray derived from pheromones (chemicals emitted by animals when they are trying to attract a mate) may be beneficial in relieving symptoms of premenstrual syndrome (PMS) (Los Angeles Times, January 17, 2003).

10/9/ Recitation TA: Dongmei Li Questions a. Describe how you might design an experiment using 100 female volunteers who suffer from PMS to determine whether the nasal spray reduces PMS symptoms. b. Does your design from Part (a) include a placebo treatment? Why not why not? c. Does your design from Part (a) involve blinding? Is it single-blind or double-blind? Explain.

10/9/ Recitation TA: Dongmei Li Answer to 2.49 a. Randomly divide into two groups of 50, one group gets PH50 (contain pheromone) and the other group gets a placebo nasal spray. Assess before and after the treatment, measure improvement. It would be more accurate if neither the subjects or the assessors and recorders of the PMS symptoms knew which treatment group each subject had been assigned. b. A placebo treatment is needed to see if any improvement is due to PH50 or to any other influence that occurs during the time of testing. c. Double-blinding, as described in a, would be advisable.

10/9/ Recitation TA: Dongmei Li 2.62 on page 67 According to the article “Effect of Preparation Methods on Total Fat Content, and Sensory Characteristics of Breaded Chicken Nuggets and Beef Steak Fingers” (Family and Consumer Sciences Research Journal [1999]: 18-27), sensory tests were conducted using 40 college student volunteers at Texas Women’s University. Given three reasons, apart from the relatively small sample size, why this sample may not be idea as the basis for generalizing to the population of all college students.

10/9/ Recitation TA: Dongmei Li Answer to 2.62 Firstly, the sample consists of only women and male responses may be different from the women’s responses. Secondly, the participants are all volunteers and volunteer responses usually differ from those who choose not to participate. Thirdly, the participants are all from the same university which may not be representative of the entire nationwide college population.