Data for Exercise

Data Set

Description

Youth.sav

These data are from a random sample of students from schools in a southern state. Although not representative of the United States, it covers a variety of important delinquent behaviors and peer influences.

Variables for Exercise

Variable Name

Description

D1

A binary variable based on the number of delinquent acts a respondent reported. A 0 indicates that the respondent reported 1 or fewer acts, whereas a 1 indicates 2 or more acts.

Lowcertain_bin

Binary indicator of whether respondents felt there was certainty that they’d be punished for delinquent behaviors. 1 = low certainty, 0 = high certainty.

Gender

The gender of the respondent where 1 = male and 0 = female.

V2

Age of the respondent in years.

Moral

A scale that measures whether respondents thought delinquency was morally wrong. High values indicate that delinquency is viewed as morally wrong.

Delinquency

A scale indicating the number of delinquent acts that an individual reports participating in.

Studyhard

Binary indicator of studying behavior of respondents where 0 = studies less than 8 hours per week and 1 = studies 8 or more hours per week.

1. Are delinquent teens more likely to be older than teens who don’t report delinquency? One way to look at this question is with a t test. In this case, we’ll compare the mean age for delinquent students with the mean age of non-delinquent students:

a. State research and null hypotheses for this topic.

b. What type of test should you use: an independent-samples t test or a matched-group test?

c. For this analysis, use an alpha of .001 for your significance level.

d. Conducting an independent-samples t test in SPSS: To run a t test in SPSS, select analyze->compare means-> independent-samples t-test. Put the variable “V2” (age) in the “test variable” box. Click “define groups” and enter 0 in one box and 1 in the other. Then, put our grouping variable, “D1,” in the “grouping variable” box. Select Ok:

i. The output for this needs some explanation. The first box that comes out tells you the number of cases in each group (n) and the mean and standard deviation for each group. The second box has two rows that correspond to t tests conducted with equal or unequal variances assumed. Levene’s test for equality of variances is an F test comparing group variances that will be addressed in a later question. You are interested in the columns labeled “T” and “sig. 2-tailed”; these are your test statistic and its exact p value. Also of interest is the “mean difference” box, which contains the value for the mean of group 1 minus the mean of group 2.

e. Assume that a difference of .15 in standard deviation is evidence that you have unequal variances. After looking at the standard deviations for either group, do you conclude that these groups have equal or unequal variances?

f. By using the appropriate variance assumptions, what do you conclude about the null hypothesis?

g. Write a sentence explaining what this result tells us about delinquency in substantive terms.These data are from a random sample of students from schools in a southern state. Although not representative of the United States, it covers a variety of important delinquent behaviors and peer influences.