The results of a quadratic model fit to time series data were $\tilde { y } _ { t }$ = 8.5 - 0.25t + 2.5t²,where t = 1 for 1998.The forecasted value for 2005 is 129.25.

Question

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The forecasted value for 2005 is calculated by substituting t = 8 (since 2005 is 8 years after 1998) into the equation: $\tilde { y } _ { t }$ = 8.5 + 0.25(8) + 2.5(8^2) = 8.5 + 2 + 160 = 170.5, not 129.25.

The Results of a Quadratic Model Fit to Time Series y~t\tilde { y } _ { t }y~​t​

The Results of a Quadratic Model Fit to Time Series $\tilde { y } _ { t }$