为什么会出现这样的协整结果,在STATA中:
xtwest lnpht cpi lnwt i ri g, lags(1)
With 1 lag(s), 0 lead(s) at least 20 observations are required.
Following series do not contain sufficient observations.
----------------------
city | Freq.
----------+-----------
1 | 13
2 | 13
3 | 13
4 | 13
5 | 13
6 | 13
7 | 13
8 | 13
9 | 13
10 | 13
11 | 13
12 | 13
13 | 13
14 | 13
15 | 14
16 | 13
17 | 13
18 | 13
19 | 14
20 | 13
21 | 13
22 | 14
23 | 14
24 | 14
25 | 13
26 | 13
27 | 13
28 | 13
29 | 13
30 | 13
31 | 13
32 | 13
33 | 14
34 | 13
35 | 13
----------------------
.