Exam 10: Designing, Conducting, Analyzing, and Interpreting Experiments With Two Groups

The assumption that the variances are equal for the groups you plan to compare statistically is known as

Distinguish between random assignment and random selection. Why is random assignment important in an experiment?

Beth is interested in studying the effects of movies on peoples' attitudes toward the mentally ill. She obtains a sample of college students who have never seen One Flew Over the Cuckoo's Nest. Half of the students watch the movie and half do not, and then she measures their attitudes toward the mentally ill. She is worried that if participants have a loved one who is mentally ill, they may have different attitudes from everyone else. She decides to give a pretest to determine if people have family members with a mental illness to make sure that there are equal numbers of such people in both the experimental and control groups. Beth is using

Research participants in a two-group design who are naturally related in some way (e.g., twins) are referred to as

Error variability consists of

Questions refer to the following computer output in which a researcher compared the GPA of traditional (aged 18-22) and nontraditional (aged 23 or older) students. Table 10-1 GROUP $1 =$ Aged $18 - 22$ GROUP $2 =$ Aged 23 or older Variable $=$ Grade point average GROUP N Mean SD Standard Error GROUP 1 15 2.95 0.556 0.143 GROUP 2 15 3.08 0.524 0.135 $F _ { \max }$ test $\quad F = 0.225 \quad p = 0.639$ Equal Variances Assumed $t = - 0.68 \quad d f = 28 \quad p = 0.509$ Equal Variances Not Assumed $t = - 0.68 \quad d f = 27.90 \quad p = 0.509$ -Consult Table 10-1. The data indicate ________ of variance; therefore, we should use the output under _________________.

For a correlated-groups t test, why do you want the paired scores to be positively correlated?

Tim measured classroom behaviors both before and after administering a family systems intervention to a sample of children. Tim used a(n) _________ design and should analyze his data using a(n) _____________samples t test.

The differing amounts of the IV are referred to as

What are the two primary advantages of correlated-groups designs?

Suppose you know that you would like to conduct a study with one independent variable. What is the next question that you face?

You should use a correlated samples t test when

What is the difference between random assignment and correlated assignment?

Understanding Experiments with Two Groups - Answer Key Twenty sets of depressed twins are obtained for a study on the effects of a new antidepressant. In each twin set, one twin is assigned to receive the drug, and the other is designed to receive the placebo. Three months later, depression levels are measured on a scale from 1 (not at all depressed) to 7 (very depressed). The following data was obtained: GROUP $1 =$ Received drug GROUP $2 =$ Received placebo Variable $=$ Depression level GROUP N Mean SD GROUP 1 10 3.21 1.035 GROUP 2 10 5.77 1.772 t=5.785 df=9 p=0.017 Cohen's d=.88 -What is the independent variable?

Candace compares the reaction times of people diagnosed with obsessive-compulsive disorder and people not diagnosed with obsessive-compulsive disorder. Candace has conducted a(n)

What is matched pairs? Why would a researcher choose to do matched pairs instead of random assignment? What is one potential problem with matched pairs?

Why is random assignment important?

What is the most basic experimental design?

Undesired variables that may influence the DV and thus invalidate the experiment are known as _________ variables.

Which of the following is NOT a way to use correlated assignment?