A researcher is interested in characteristics of HIV+ and HIV- adolescents interviewed 166 young adults about their experiences during adolescence. He wished to know, among other things, if there were significant differences in the ages at which HIV+ and HIV- young adults became sexually active. The following is the printout of this analysis:
HIV Status N Mean sd Stnd. Error
Age at Positive 57 13.2 2.96576 .39282
first sexual
experience Negative 109 15.1 2.57286 .24644
Independent Samples Test
Levene's Test for
Equality of Variances
F Sig
Age at Equal variance assumed 1.313 .254
first sexual
experience Equal variance not assumed
t-test for Equality of Means
t df sig. mean difference
Age at Equal variance assumed -2.870 164 .005 -1.9
first sexual
experience Equal variance not assumed -2.745 99.66 .007 -1.9
1. Were there significant differences between the groups. Give the relevant stastical data to support your answer?
2. What is the confidence interval associated with your answer to item 1?
Each of the questions on the following pages is a calculation problem worth 10 points. Partial credit will be awarded if I can following your procedures and determine that errors are arithmetic rather than conceptual. It would be wise, therefore, to clearly indicate your worksteps on each problem.
3. For the following data set, calculate the oneway ANOVA and test for significance at the .05 level.
Group 1 Group 2 Group 3 Group 4
x x^{2} x x^{2} x x^{2} x x^{2}
7 49 10 100 12 144 16 256
8 64 12 144 14 196 15 225
7 49 13 169 13 169 18 324
9 81 13 169 11 121 17 289
9 81 14 196 13 169 20 400
11 121 15 225 15 225 21 441
10 100 14 196 13 169 22 484
61 545 91 1,199 91 1,193 129 2,419