Question

SPSS Portion

Here you analyze T tests in SPSS, and interpret output.  

Part I Independent Sample (8 points) (part 2 is below)

There is research being conducted on chow for small dogs. Below are the comparison between weights (wt) of a group of dogs with normal food and with the special food. Group 1 is the group that had the Normal Diet, and Group 2 is the group that had the Special Diet.

Wt Group

4 1

6 1

5 1

5 1

6 1

5 1

4 1

6 1

5 1

4 1

9 2

8 2

6 2

8 2

5 2

6 2

8 2

7 2

4 2

5 2

Once you have entered the data,  

• In SPSS go to Analyze: Compare Means: Independent Samples.

• You will see a dialogue box that says test variables and grouping variables.

• Click on the weight variable to go in the test variable box, and the group variable to go in the grouping variable box.

• Under the grouping variable box you will see where it says “define groups?” Click on that.   

• Another dialogue box will open which says “user specified values.”

• Put a 1 in group 1 and a 2 in group 2 (you have just told the program that your data is divided into two groups, and that the groups are identified with the number 1 and the number 2.) Then hit OK.,. An output box will open. Copy and paste that output into your hw doc.

Use the output to respond to the following questions:

16. Looking at the group statistics box, what is the mean and standard deviation for weight in group one and group two? (1 points)

17. Look at the next box that says Independent Samples Test. Ignore the first few columns about Levene’s equality of variances—this is not the outcome of the t test, you don’t need to focus on that right now. Go right to the INDEPENDENT SAMPLES t TEST COLUMN.

a. What are the t and the df in the first row of data in this box? (2 pts)

b. What is the significance level? What does this mean about whether we are “in” the null distribution? (2 pts)

c. Are the weights for the Normal and Special diets different or not different, according to this test? (1 pt)

d. What is the 95% confidence interval for the difference (it is in the output!), and what do these numbers mean in words? (2 pts)

Answer 1

a)
t = -2.753 , df = 18

b)
significance level = 0.05

c)
since p-value = 0.013 < alpha
hence we reject the null hypothesis
we conclude that weights for the Normal and Special diets are significantly different

d)
95 % CI = (-2.82103,-0.37897)
it means we are 95 % confident that the true difference in means lies between this CI