To test an herbal treatment for depression, 100 volunteers who suffered from mild depression were randomly divided into two groups. Each person was given a month's supply of tea bags. For one group, the tea contained the herb mixed with spice tea, whereas for the other group, the bags contained only the spice tea. Participants were not told which type of tea they had, and were asked to drink one cup of tea per day for a month. At the end of the month, a psychologist evaluated them to determine if their mood had improved. The psychologist did not know which of the subjects had the tea with the herbal ingredient added. Which is true regarding this study? This study is an observational study. This study is double-blind. The "only spice tea" group serves as the control group. All of the above are true. O Only (B) and (C) are true.Students in a large statistics class were randomly divided into two groups. The first group took the midterm exam in a room painted in pale green while the second group took the exam in a room painted bright yellow. The exam scores ofthe two groups were then compared. This experiment was not blind because: the students knew which color the room in which they took the exam was painted. students were randomized into the two groups. the exam was too long. some of the students did not study for the exam. OOOOO students were allowed to keep their eyes open while taking the exam. The main advantage of experiments over observational studies is that: a well-designed experiment can give good evidence that the treatment actually causes the response. an experiment can compare two or more groups. an experiment is always cheaper. an experiment is always shorter. OOOOO we can include more than one explanatory variable in the study. IQ has been used to predict academic success. But what about other factors? According to an article by Angela L. Duckworth and Martin E.P. Seligman in thejournal Psychological Science, self-discipline is even a better predictor ofacademic success than IQ. One way to measure self-discipline is the $1-now or $2-Iater test (which the researchers call the Delay Choice Task) in which we see ifa subject would decline to accept a dollar bill now when told they could wait a week and get two dollars. Highly self-disciplined adolescents outperformed their more impulsive peers on every academic-performance variable, including report card grades. Which of the following is correct? 0 This study is an experiment, since it was based on a random sample. C) This study is an observation study since the researchers did not assign the students to one of the self-discipline categories. 0 This study is an experiment, since each subject was classified into a self-discipline category ($1-n0w or $2-later) and to report card grades. 0 This study is a combination of both an experiment and an observational study. In an experiment to see ifa new medication reduces the duration a headache, a placebo is: a dummy pill that looks like the new medication but has no active ingredients. a procedure for deciding who gets the new medication. the place where the subjects go when they have a headache. the randomization procedure. 00000 the sampling method. For their 1992 study "The Effect of Country Music on Suicide" (published in Social Forces, vol. 71, p. 21 I), researchers Stack and Gundlach investigated various American communities, recording the number of minutes of daily radio airtime devoted to country songs and the suicide rate. They found a moderately strong positive correlation. In their paper, the researchers explain the results by saying that "...the themes found in country music fostera suicidal mood (emphasis added). A news headline (The Independent [London], October 1, 2004, p. 15) about the research echoed these sentiments when it said, "Strange But True: Country Music Saps Will to Live." The research is even cited on various suicide-prevention websites, some with headings such as "Country Music Increases Suicide Risk." Based upon this study, can we have confidence that country music has a causal effect on suicide? 0 Yes, as long as the communities were sampled randomly, and the number of communities (the sample size) was sufficiently large. Q Yes, causality is indicated by the moderately strong correlation. Q Yes, since different communities listened to different levels of country music, meaningful experimental comparisons can be made. 0 No, because the lack of assignment of communities to different levels of country music listening means there is a possibility of lurking variables. O No, causality can only be demonstrated by investigating the entire population. The most important reason for the use of random allocation of subjects to the different treatments is: to ensure that each subject in the trial receives the best possible treatment. to guarantee that approximately the same number of subjects is assigned to each treatment group. to protect the experimenters from legal action in the event that the experiment goes drastically awry. 0000 to ensure that the different treatment groups are as similar as possible in every way exceptfor the treatment received. 0 to guarantee that the results of the experiment can never be duplicated