Molly McPup

Introduction to Research Methods in Political Science:
The POWERMUTT* Project
(for use with SPSS)

*Politically-Oriented Web-Enhanced Research Methods for Undergraduates — Topics & Tools
Resources for introductory research methods courses in political science and related disciplines

SITE
MAP

CORRELATE
 
From the menu bar, click on “Analyze,” then on “Correlate,” and on “Bivariate….”   In the left window, select the variables you wish to analyze, and click on the top right arrow.  Select one or more of the correlation coefficients.  The default is Pearson’s r.  Select either a one or two-tailed test of statistical significance.  The default is a two-tailed test, but a one-tailed test is appropriate for hypotheses that predict whether a relationship will be positive or negative.  Since this will usually be the case, you will probably want a one-tailed test.
 
Click on “Options….”  You may select any the optional statistics that are available.  By default, CORRELATE provides for pairwise deletion of missing data.  You may instead select listwise deletion.  Pairwise deletion means that each correlation will be based on all case with non-missing values for the two variables in question.  This has the advantage of using as much information as possible for the calculation of each coefficient.  The disadvantage is that the coefficients may not be based on the same subset of cases, since different cases may be missing data for different variables.   Listwise deletion means that if a case has missing data for any of the variables in the correlation matrix, it will be deleted from all calculations.  This insures that all coefficients will be based on the same cases, but will eliminate a case from all calculations even if it is missing data for only one or two variables in the correlation matrix.  If you only have a small proportion of missing data, it will not make much difference which option you choose.  If you have a lot of missing data, neither option is very satisfactory. 
 
When you have finished selecting your options, click on “Continue” and on “OK.”
 
Output will be in the form of a matrix showing the correlation between each variable you have selected and every other variable.  For each correlation, you will also be given the number of cases on which it is based and the significance level.  If the significance level is given as “.000” this does not really mean that there is a zero probability of the relationship occurring by chance.  Rather, it means that the probability is less than .0005.

 


Last updated April 28, 2013 .
© 2003---2013  John L. Korey.  Licensed under a  Description: Creative Commons License Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.