NO.PZ201904080100008001
问题如下：
1. The 95% confidence interval for b0 is closest to:
Give the t-critical values as follow:
the t-critical values are all two-tails
选项：
A.
-0.0032 to +0.01375
B.
-0.0016 to +0.0025
C.
0.0008 to +0.01375.
D.
-0.0032 to +0.01378
解释：
A is correct.
考点：Confidence Interval in Linear Regression
解析：因为是48个月的数据，所以n=48，所以本题应该去查双尾95%的df=48-2=46的数据，即 the critical two-tailed 95% t-value = 2.013.
所以b0的95%的置信区间应该为 (0.0053-0.0042*2.013, 0.0053+0.0042*2.013) = (-0.0032, 0.01375)
是不是Y的df=n-1，X的df=k，∈的df=n-k-1，所有b的df=n-k-1
