cnl 540 3.2

What was the independent variable in this experiment?

Social psychologists at the University of California at Berkeley wanted to study the effect that staring at drivers would have on driver behavior (Ellsworth, Carlsmith, and Henson, 1972).  In a randomized experiment, the researchers either stared or did not stare at the drivers of automobiles stopped at a campus stop sign.  The researchers timed how long it took each driver to proceed from the stop sign to a mark on the other side of the intersection.  Suppose that the random sample of crossing times, in seconds, gave the following output: Group                   N                  Mean             StDev No Stare               14                    6.63                 1.360  Stare                     13                    5.59                 0.822 Construct a 95% confidence interval for the difference in stop times.

3. A researcher was interested in the effects of a drug on depression. Subjects were randomly assigned to one of the three groups. Subjects in the control group received a placebo and the subjects in the two treatment groups received either a 0.2 mg or a 0.4 mg dosage of the drug. After several weeks of drug (or placebo) treatment, the researcher measured the subjects' level of depression (a low score indicating greater depression) The following data were obtained. Placebo 0.2 mg 0.4 mg 12 11 12 10 9. 14 11 11 17 13 13 16 15 7 16 12 Mean of X = 10 14 12 S^2 = 5.6 8.4 Using 5% of significance, test the hypothesis that the three groups differ in their effectiveness.

A sociologist wants to investigate the question, "Is there a relationship between texting during class and grade-point-average (GPA) among high school seniors in a large district?" Which study design is most appropriate?     Before the semester starts, randomly select 40 seniors from each high school who do not text during class. Assign 20 to the texting treatment group (text three or more times during every class meeting) and 20 to the control group (no texting during class). At the end of the semester, obtain each student’s GPA from the appropriate admissions and records office. Compare the GPA of students who routinely text during class to the GPA of students who do not text during class. Before the semester starts, randomly select 40 seniors from each high school who do not text during class. Assign 20 to the texting treatment group (text three or more times during every class meeting) and 20 to the control group (no texting during class). At the end of the semester,…

When two independent variables produce effects when combined that would not be present if each independent variables was manipulated in a separate study, we say that there is O no main effect. O only a measured variable an interaction. O a planned comparison. rist and Stangor (2001) studied prejudice and found that you can't predict a person's behavior toward minorities on the basis of whether they are high or low

The director of student services at Oxnard College is interested in whether women are just as likely to attend orientation as men before they begin their coursework. A random sample of freshmen at Oxnard College were asked what their gender is and whether they attended orientation. The results of the survey are shown below: Data for Gender vs. Orientation Attendance Women Men Yes 440 410 No 238 239 What can be conduded at the a - 0.10 level of significance? For this study, we should use z-test for a population proportion a. The null and alternative hypotheses would be: Ho: Select an answer v Select an answer v Select an answer v (please enter a decimal and note that p1 and ul represent the proportion and mean women and and u2 represent proportion and mean for men.) H: Select an answer v Select an answer v Select an answer v (Please enter a decimal) b. The test statistic ? v (please show your answer to 3 decimal places.) c. The p-value = (Please show your answer to 4 decimal places.) d.…

It is common for baseball pitchers to use stretching to prepare for a game. But does this make a difference? The authors of a paper on the effects of stretching in baseball carried out an experiment to compare two different types of stretching and a control treatment consisting of no stretching. Participants were adult males with varying levels of baseball throwing experience and who were not professional or collegiate baseball players. Participants in the two stretching treatments went through a warm-up that included 8 minutes of stretching. Each participant (all three groups) then threw 10 pitches, and the average speed (km/hour) was calculated. (a) Explain why it is important that the participants be assigned at random to the three different treatment groups (Stretching Method 1, Stretching Method 2, and No Stretching). Random assignment ensures that our experiment systematically favors one experimental condition over all others and attempts to create experimental groups that are as…

introduces a study investigating whether a brief diet intervention might improve depression symptoms. In the study, 75 college-age students with elevated depression symptoms and relatively poor diet habits were randomly assigned to either a healthy diet group or a control group. Depression levels were measured at the beginning of the experiment and then again three weeks later. The response variable is the reduction in depression level (as measured by the DASS survey) at the end of the three weeks. Larger numbers mean more improvement in depression symptoms. Test whether these experimental results allow us to conclude that, on average, improvement of depression symptoms is higher for those who eat a healthy diet for three weeks than for those who don't. The data is available on StatKey and in DietDepression. Let Group 1 represent those with a healthy diet and Group 2 represent those with no diet change. State the null and alternative hypotheses.