The physical dataset on the companion website gives heights (inches) and head circumferences (cm) for a sample of college students. For females only, the correlation between the two variables is 0.05, while for males only, the correlation is 0.19. For the combined sample of males and females, however, the correlation is 0.42. Explain why the correlation in the combined sample is higher than the correlations in the separate samples of males and females. Refer to given Example for guidance.
Example
Does It Make Sense? Height and Lead Feet For a sample of college students, a scatterplot of their heights and their responses to the question "What is the fastest you have ever driven a car?" is displayed in given Figure.
