Aa Aa E 9. The point-biserial correlation Suppose a social psychologist sets out to see whether the age of entering the relationship is related to relationship longevity. He decides to measure relationship satisfaction in a group of couples formed when the younger partner was younger than 30 and a group of couples formed when the younger partner was 30 or older. He chooses the Marital Satisfaction Inventory because it refers to partner" and "relationship" rather than "spouse" and "marriage," which makes it useful for research with both traditional and nontraditional couples. Higher scores on the Marital Satisfaction Inventory indicate greater relationship satisfaction. The psychologist administers the Marital Satisfaction Inventory to 85 couples-31 are couples formed when the younger partner was younger than 30 and 54 are couples formed when the younger partner was 30 or older. He wants to calculate the correlation between a couple's relationship satisfaction and whether the younger partner was younger or older than 30 at the beginning of the relationship. Which of the following types of correlations would be most appropriate for the psychologist to use? A Pearson correlation A point-biserial correlation A phi-Coefficient A Spearman correlation To calculate the correlation, the psychologist converts "the age of entering the relationship to a dichotomous variable. Suppose the data for the first 5 couples he surveys are shown in the table that follows. By assigning zero (0) to couples formed when the younger partner was younger than 30 and one (1) to couples formed when the younger partner was 30 or older, complete the table. Marital Satisfaction Age of the Younger Partner Age of the Younger Partner Inventory Score (Converted) younger than 30 20 younger than 30 41 30 or older 18 30 or older 46 younger than 30 32 Suppose the psychologist calculates the correlation using the data as coded in the previous table. Then, he recalculates the correlation, but this time, instead of assigning zero (0) to couples formed when the younger partner was younger than 30 and one (1) to couples formed when the younger partner was 30 or older, he reverses the codes and assigns one (1) to couples formed when the younger partner was younger than 30 and zero (O) to couples formed when the younger partner was 30 or older. Which of the following statements is true regarding his two calculations of the correlation? The signs of the two correlations are opposite, but their absolute values are the same. The absolute values of the two correlations are different. The two correlations are the same. Before calculating the correlation, the psychologist does an independent-measures t test comparing the Marital Satisfaction Inventory scores of couples formed when the younger partner was younger than 30 and couples formed when the younger partner was 30 or older. The value of the t statistic is 2.63 with 83 degrees of freedom. Using this Information, the square of the point-biserial correlation is 2
