You cannot "predict" accurately the future values using this. It's important to note that curve fitting really only works within the bounds of data that you've entered. This means that you should do an exponential curve fitting (Unless it's a linear decrease which it's not): I don't know how you got that equation in Excel as this is the equation that I get:Ĭheck to make sure that the degree of polynomial is 2 and that you haven't set any intercepts or forecasts into the trend-line creation.Īnother thing, you said, x increases and y decreases. Here's the real equation that fits this data: But when I use that equation, it doesn't produce those outputs for those inputs.Įdit: or is it excel? Here's the graph of that equation (above):Ĭlearly that is not trending downward for the range 300-390. That produces the equation above, with an R^2 value of. ![]() select Series1 and add a polynomial (2) trendline, display equation, display R-squared.The equation is 0.0096x2 - 0.4181x + 13.341 When I plug in x values to that equation, the numbers go up! So something is pretty wrong here. But when I do a polynomial regression on these data, even though the trendline matches the data pretty well, the equation it generates doesn't work. I'd like to use these data to derive an equation using Excel.
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