User manual SPSS BASE 11.5

[. . . ] SPSS Base 11. 5 User's Guide ® For more information about SPSS® software products, please visit our Web site at http://www. spss. com or contact SPSS Inc. 233 South Wacker Drive, 11th Floor Chicago, IL 60606-6412 Tel: (312) 651-3000 Fax: (312) 651-3668 SPSS is a registered trademark and the other product names are the trademarks of SPSS Inc. No material describing such software may be produced or distributed without the written permission of the owners of the trademark and license rights in the software and the copyrights in the published materials. Use, duplication, or disclosure by the Government is subject to restrictions as set forth in subdivision (c)(1)(ii) of The Rights in Technical Data and Computer Software clause at 52. 227-7013. [. . . ] Tests: Levene's test for equality of variances, and both pooled- and separate-variances t tests for equality of means. The values of the quantitative variable of interest are in a single column in the data file. The procedure uses a grouping variable with two values to separate the cases into two groups. The grouping variable can be numeric (values such as 1 and 2, or 6. 25 and 12. 5) or short string (such as yes and no). As an alternative, you can use a quantitative variable, such as age, to split the cases into two groups by specifying a cut point (cut point 21 splits age into an under-21 group and a 21-and-over group). For the equal-variance t test, the observations should be independent, random samples from normal distributions with the same population variance. For the unequal-variance t test, the observations should be independent, random samples from normal distributions. When checking distributions graphically, look to see that they are symmetric and have no outliers. Sample Output Figure 20-1 Independent-Samples T Test output Group Statistics Std. Error Mean 5. 39 4. 31 N Blood pressure Treatment placebo new_drug 10 10 Mean 142. 50 116. 40 305 T Tes ts Independent Samples Test Levene's Test for Equality of Variances t-test for Equality of Means 95% Confidence Interval of the Mean Lower 11. 61 Upper 40. 59 F Blood pressure Equal variances assumed Equal variances not assumed . 134 Significance . 719 t 3. 783 df 18 Significance (2-tailed) . 001 Mean Difference 26. 10 Std. Error Difference 6. 90 3. 783 17. 163 . 001 26. 10 6. 90 11. 56 40. 64 To Obtain an Independent-Samples T Test From the menus choose: Analyze Compare Means Independent-Samples T Test. . . Figure 20-2 Independent-Samples T Test dialog box Select one or more quantitative test variables. A separate t test is computed for each variable. 306 Chapter 20 Select a single grouping variable, and click Define Groups to specify two codes for the groups that you want to compare. Optionally, you can click Options to control the treatment of missing data and the level of the confidence interval. Independent-Samples T Test Define Groups Figure 20-3 Define Groups dialog box for numeric variables For numeric grouping variables, define the two groups for the t test by specifying two values or a cut point: n Use specified values. Numbers need not be integers (for example, 6. 25 and 12. 5 are valid). n Cut point. Alternatively, enter a number that splits the values of the grouping variable into two sets. All cases with values less than the cut point form one group, and cases with values greater than or equal to the cut point form the other group. Figure 20-4 Define Groups dialog box for string variables For short string grouping variables, enter a string for Group 1 and another for Group 2, such as yes and no. Cases with other strings are excluded from the analysis. 307 T Tes ts Independent-Samples T Test Options Figure 20-5 Independent-Samples T Test Options dialog box Confidence Interval. By default, a 95% confidence interval for the difference in means is displayed. Enter a value between 1 and 99 to request a different confidence level. When you test several variables and data are missing for one or more variables, you can tell the procedure which cases to include (or exclude): n Exclude missing data analysis by analysis. Each t test uses all cases that have valid data for the variables tested. Each t test uses only cases that have valid data for all variables used in the requested t tests. [. . . ] Click Paste. 582 Chapter 46 Note: You must use the script window menus to open the dialog box; otherwise, commands will be pasted to a syntax window rather than the scripting window. Running a Script from Command Syntax You can use the SCRIPT command to run a script from within command syntax. Specify the name of the script you want to run, with the filename enclosed in quotes, as follows: SCRIPT 'C:\PROGRAM FILES\SPSS\CLEAN NAVIGATOR. SBS'. Appendix A Database Access Administrator The Database Access Administrator is a utility designed to simplify large or confusing data sources for use with the Database Wizard. It allows users and administrators to customize their data source in the following ways: n Create aliases for database tables and fields. n Hide extraneous tables and fields. The Database Access Administrator does not actually change your database. [. . . ]