Child Development 133 
Research Methods in Human Development

Sections 02 & 06
Hembree            Fall, 2009

 

Homework #6 - Problem Set II

Due 10/29 - 8 points

See text,  t-test handout and Chi-square handout.

1) A researcher decides to test the effectiveness of three different therapies for reducing depression. He randomly assigns a sample of severely depressed individuals to one of three therapy groups. At the conclusion of the therapy sessions, he obtains the following depression scores (lower scores indicate lower reported depression):

      Therapy A                                            Therapy  B                              Therapy C

10                                                        14                                            20

12                                                        16                                            18

16                                                        15                                            19

12                                                        12                                            15

13                                                        18                                            16

14                                                        17                                            20

12                                                        13                                            13

18                                                        14                                            15

10                                                        13                                            16

13                                                        18                                            18

 

 

 

1a) Compute the mean, variance, and standard deviation for each group.

 

1b) Using a t-test, test whether therapy A resulted in lower depression scores than therapy B. Using a t-test, test whether therapy A resulted in lower depression scores than therapy C. Show your work. What conclusions can you draw about the effectiveness of the different therapies? When you compute a t-test , what are you doing (conceptually)? 

 

 

 

 

 

 

 

 

 

2)  An analysis of automobile accidents was conducted to see whether large automobiles are safer than smaller ones. The data for 100 accidents are as follows: 

 

Size of automobile

 

 

 

Small

Medium

Large

 

 

        Non-Fatal

 

 

10

 

20

 

30

 

60

 

                Fatal

 

 

20

 

10

 

10

 

40

 

 

 

30

 

30

 

40

 

     100

 

Conduct a chi-square test to determine whether smaller-sized cares are more likely to be involved in fatal accidents. Show your work and be sure to indicate what your conclusion is, based on the result.  When you compute a χ2 , what are you doing (conceptually)?

 

 

 

 

 

 

 

 

 

 

 

3) What does it mean for a result to be statistically significant? What are some reasons that a result might not be significant?

 

 

 

 

 

 

 

Send problems, comments or suggestions to: hembrees@csus.edu

California State University, Sacramento
College of Education
Department of Child Development

Updated: August, 2009