19. Refer to the previous two exercises. Using software, obtain the correlation matrix for these data. Which pairs of variables are highly correlated? Describe the nature of those correlations, and explain how your software handled the missing values. (For a partic- ular analysis. most software deletes observations for which data are missing on at least one variable used in the analysis. Better strategies exist. see. for instance, R. Little and D Rubin. Sociological Methods and Research. Vol. 18. 1989. pp. 292-326)