The following time-series plot is based on data from the article “Bubble Talk Expands: Corporate Debt Is Latest Concern Turning Heads” (San Luis Obispo Tribune, Sep tem ber 13, 2002) and shows how household debt and corporate debt have changed over the time period from 1991 (year 1 in the graph) to 2002:

Based on the time-series plot, would the correlation coefficient between household debt and corporate debt be positive or negative? Weak or strong? What aspect of the time-series plot supports your answer?