Final answer:
a. The similarity between the slope of a regression line and correlation is that they both have the same sign, meaning they both indicate the direction of the relationship between the two variables.
Step-by-step explanation:
The slope of a regression line and the correlation are similar in the sense that they both have the same sign. This is because the sign of a correlation coefficient, typically represented by the letter r, indicates the direction of the relationship between two variables.
A positive r value suggests that as one variable increases, the other variable also increases, which corresponds to a positive slope in the regression line.
Conversely, a negative r value suggests that as one variable increases, the other decreases, corresponding to a negative slope of the regression line. Therefore, the correct answer to the question is a. they both have the same sign.