I am reviewing sample problems in my statistics book from college.  When I look up the percentage point for t-distribution in the appendix of the book, it lists positive values.  When I use say for example: stats.t.ppf(0.025,15), it shows -2.131, whereas, my stat book shows 2.131.  I tried other parameters and I get same values as what my stat book shows, but again the values it returns are negative.