用了ADF检验，提示观测值不够。选择summary,none intercept的话，得到如下结果,存在不存在单位根如何判断？

Pool unit root test: Summary     
Date: 07/23/08   Time: 10:11    
Sample: 1 17    
Series: 1    
Exogenous variables: None    
Automatic selection of maximum lags    
Automatic selection of lags based on SIC: -1    
Newey-West bandwidth selection using Bartlett kernel    
Balanced observations for each test     
    
   Cross- 
Method Statistic Prob.** sections Obs
Null: Unit root (assumes individual unit root process)     
PP - Fisher Chi-square  1.38629  0.5000  1  16
    
** Probabilities for Fisher tests are computed using an asympotic Chi    
        -square distribution. All other tests assume asymptotic normality.