用eviews的结果是：
   Cross-
Method Statistic Prob.** sections Obs
Null: Unit root (assumes common unit root process)     
Levin, Lin & Chu t*  0.04515  0.5180  28  112
   
Null: Unit root (assumes individual unit root process)     
Im, Pesaran and Shin W-stat   3.26685  0.9995  28  112
ADF - Fisher Chi-square  11.2922  1.0000  28  112
PP - Fisher Chi-square  8.74118  1.0000  28  112
   
Null: No unit root (assumes common unit root process)     
Hadri Z-stat  10.2082  0.0000  28  140
用stata：
Levin-Lin-Chu test for p      Deterministics chosen: constant
Reducing Andrews truncation
Pooled ADF test, N,T = (30,5)     Obs = 120   
Augmented by 0 lags (average)     Truncation: 2 lags
coefficient    t-value        t-star       P > t
-0.76520       -9.962      -6.85181      0.0000
eviews结果表明存在单位根，而stata却显示没有，为什么会出现这种结果呢？stata中给出的Reducing Andrews truncation是什么意思啊？感谢各位大侠的解惑啊