Final answer:
Situations 1 and 2, where the dependent variable decreases as the independent variable increases or the dependent variable increases as the independent variable decreases, can result in a regression line with a negative y-intercept. This negative y-intercept indicates the starting value of the dependent variable is below zero when the independent variable is at zero.
Step-by-step explanation:
A regression line with a negative y-intercept can occur in various scenarios, typically when the plot of data points for the two variables of interest suggests that the dependent variable starts below the origin (where both dependent and independent variables are zero) when extending the line of best fit backwards. Here are the situations from the ones provided:
- The dependent variable decreases as the independent variable increases (scenario 1).
- The dependent variable increases as the independent variable decreases (scenario 2).
Both these scenarios can result in a negative y-intercept. For example, the relationship between price and quantity demanded often has a negative slope, indicating that as the price increases, consumers purchase less, which could result in a regression line that would intercept the y-axis below zero if the relationship is linear and extended back to where the price would theoretically be zero.