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excelexcel-formulaforecasting

Why do I get wrong prediction when using this polynomial forecasting formula

I would like to do a forecasting on a growth per period.

I have a formula of polynomial regression
y = -5E-05x2 + 0.0348x + 0.7148.

I translated it to: =EXP(-5)-0.5*(B4)^2+0.0348*B4+0.7148
where B4 is the period running number (I have 365 days, so B4 is the first period ,C4is the next period etc)

I have strange results (my prediction decreases over time instead of getting increased) so I guess I didn't interpret Excel's formula well.

How can I resolve this problem?

An image of the chart and Excel's formula:

enter image description here

Solution

  • -5E-05 isn't exp(-5)-5

    it is -5 * 10^(-5)

    for clarification: -7E-05 means: -7 * 10^(-5) = -.00007