I plotted some population numbers against census year and used a quadratic line of best fit resulting in an R-Sq of 99.9%.

But I'm having difficulty using the equation of the line Minitab gives:

Population = -2.90E+08 + 290872 Year - 72.87 Year**2

Solving for year 2007 in excel using =(EXP(-2.9))+290872*2007-72.87*2007^2
gives 290256173.4, which is not right because the previous year's population count was only 38,076.

Can you see where I might have gone wrong?

Cheers

I thnk that -2.90E+08=-2.9*(10^8)

But -2.9*10^8-290872*2007-72.87*2007^2 = -1167304035

My calculator gives 36599 for 2007 (using quadratic reg) :confused: