0.0009不除以n开根吗？

问题如下：

Based on Exhibit 1, Olabudo should calculate a prediction interval for the actual US CPI closest to:

选项：

A. 2.7506 to 2.7544

B. 2.7521 to 2.7529

C. 2.7981 to 2.8019

解释：

A is correct. The forecast interval for inflation is calculated in three steps:

Step 1. Make the prediction given the US CPI forecast of 2.8:

${\rm{\hat Y=}}{{\rm{b}}_{\rm{0}}}{\rm{+}}{{\rm{b}}_{\rm{1}}}{\rm{X = 0}}{\rm{.0001+(0}}{\rm{.9830}}\times{\rm{2}}{\rm{.8)=2}}{\rm{.7525}}$

Step 2. Compute the variance of the prediction error:

$s_f^2=s_e^2\left\{{1+(1/n)+[{{({X_f}-\bar X)}^2}]/[(n-1)\times s_x^2]}\right\}$

$s_f^2=0.0009_e^2\left\{{1+(1/60)+[{{(2.8-1.3350)}^2}]/[(60-1)\times{{0.7539}^2}]}\right\}$

$s_f^2=0.00000088$

${s_f}=0.0009$

Step 3. Compute the prediction interval:

$\hat Y\pm{t_c}\times{s_f}$

2.7525±(2.0 x 0.0009)

Lower bound: 2.7525 - (2.0 x 0.0009) = 2.7506.

Upper bound: 2.7525 + (2.0 x 0.0009) = 2.7544.

So, given the US CPI forecast of 2.8, the 95% prediction interval is 2.7506 to 2.7544.