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Research Design Explained

Mark L. Mitchell, Janina M. Jolley

Chapter 10

The Simple Experiment - all with Video Answers

Educators

Chapter Questions

00:24

Problem 1

A professor has a class of 40 students. Half of the students chose to take a test after every chapter (chapter test condition) outside of class. The other half of the students chose to take in-class "unit tests." Unit tests covered four chapters. The professor finds no statistically significant differences between the groups on their scores on a comprehensive final exam. The professor then concludes that type of testing does not affect performance.
a. Is this an experiment?
b. Is the professor's conclusion reasonable? Why or why not?

Hossam Mohamed
Hossam Mohamed
Numerade Educator
03:00

Problem 2

Participants are randomly assigned to meditation or no-meditation condition. The meditation group meditates three times a week. The meditation group reports being significantly more energetic than the nomeditation group.
a. Why might the results of this experiment be less clear-cut than they appear?
b. How would you improve this experiment?

Beth Stone
Beth Stone
Numerade Educator
03:58

Problem 3

Theresa fails to find a significant difference between her control group and her experimental group $t(10)=2.11$, not significant. a. Given that her results are not significant, what-if anything-would you advise her to conclude?
b. What would you advise her to do? (Hint: You know that her $t$ test, based on 10 degrees of freedom, was not significant. What does the fact that she has 10 degrees of freedom tell you about her study's sample size, and what does it suggest about her study's power?)

Amany Waheeb
Amany Waheeb
Numerade Educator

Problem 4

A training program significantly improves worker performance. What should you know before advising a company to invest in such a training program?

Check back soon!
02:51

Problem 5

Jerry's control group is the football team, his experimental group is the baseball team. $\mathrm{He}$ assigned the groups to condition using random assignment. Is there a problem with Jerry's experiment? If so, what is it? Why is it a problem?

Shannon Merkle
Shannon Merkle
Numerade Educator
01:01

Problem 6

Students were randomly assigned to two different strategies of studying for an exam. One group used visual imagery, the other group was told to study the normal way. The visual imagery group scores $88 \%$ on the test as compared to $76 \%$ for the control group. This difference was not significant.
a. What, if anything, can the experimenter conclude?
b. If the difference had been significant, what would you have concluded?
c. "To be sure that they are studying the way they should, why don't you have the imagery people form one study group and have the control group form another study group?" Is this good advice? Why or why not?
d. "Just get a sample of students who typically use imagery and compare them to a sample of students who don't use imagery. That will do the same thing as random assignment." Is this good advice? Why or why not?

Kimberly Waterbury
Kimberly Waterbury
Numerade Educator
04:24

Problem 7

Bob and Judy are doing the same study, except that Bob has decided to put his risk of a Type 1 error at .05 whereas Judy has put her risk of a Type 1 error at .01. (Note that consulting Table 1 in Appendix $\mathrm{F}$ will help you answer parts a and b.)
a. If Judy has 22 participants in her study, what $t$ value would she need to get significant results?
b. If Bob has 22 participants in his study, what $t$ value would he need to get significant results?
c. Who is more likely to make a Type 1 error? Why?
d. Who is more likely to make a Type 2 error? Why?

Ramon Kryzhan
Ramon Kryzhan
Numerade Educator
00:51

Problem 8

Gerald's dependent measure is the order in which people turned in their exam (first, second, third, etc.). Can Gerald use a $t$ test on his data? Why or why not? What would you advise Gerald to do in future studies?

Sheryl Ezze
Sheryl Ezze
Numerade Educator
02:41

Problem 9

Are the results of Experiment A or Experiment B more likely to be significant? Why?
$$
\text { EXPERIMENT A }
$$
$$
\begin{array}{cc}
\hline \text { Control group } & \text { Experimental group } \\
\hline 3 & 4 \\
\hline 4 & 5 \\
\hline 5 & 6
\end{array}
$$
$$
\text { EXPERIMENT B }
$$
$$
\begin{array}{cc}
\hline \text { Control group } & \text { Experimental group } \\
\hline 0 & 0 \\
\hline 4 & 5 \\
\hline 8 & 10
\end{array}
$$

Asma Venkitta
Asma Venkitta
Numerade Educator
02:51

Problem 10

Are the results of Experiment A or Experiment B more likely to be significant? Why?
$$
\text { EXPERIMENT A }
$$
$$
\begin{array}{cc}
\hline \text { Control group } & \text { Experimental group } \\
\hline 3 & 4 \\
\hline 4 & 5 \\
\hline 5 & 6
\end{array}
$$
$$
\text { EXPERIMENT B }
$$
$$
\begin{array}{cc}
\hline \text { Control group } & \text { Experimental group } \\
\hline 3 & 4 \\
\hline 4 & 5 \\
\hline 5 & 6 \\
\hline 3 & 4 \\
\hline 4 & 5 \\
\hline 5 & 6 \\
\hline 3 & 4 \\
\hline 4 & 5 \\
\hline 5 & 6
\end{array}
$$

Shannon Merkle
Shannon Merkle
Numerade Educator