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I have the following output from from R.

I know we can calculate predicted values using the predict() function.

How can we calculate the predicted value by hand if X=2 or 3?

I'm using the below formula but my answer differs from the output from the predict() function.

enter image description here

enter image description here

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  • $\begingroup$ Does this work correctly when you use a first or second order polynomial? $\endgroup$
    – James Phillips
    Commented Apr 20, 2019 at 18:52
  • $\begingroup$ No, it still does not work. Based on my understanding, if X=2, calculation should be Y=67.7944+(16.9254 *2)+(-8.5843*2^2)+(-0.8990^3). In R, the predicted value is 59.66852 but when I calculate manually, I get 66.58 $\endgroup$
    – JPGS
    Commented Apr 21, 2019 at 7:56
  • $\begingroup$ See stats.stackexchange.com/questions/31858/…. $\endgroup$
    – whuber ♦
    Commented Apr 23, 2019 at 3:44

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