我选用了12年的数据做分析，在做误差修正时滞后区间是0 2，出来的结果中 F-statistic的值都是NA ，请问是怎么回事？要是因为数据样本太短有没有别的办法？

   
 R-squared             -0.122201            -0.071824                       -0.192754
 Adj. R-squared     -0.122201             -0.071824                       -0.192754
 Sum sq. resids        0.008233             0.153636                       0.599714
 S.E. equation          0.028693             0.123950                       0.244891
 F-statistic                    NA                         NA                                 NA
 Log likelihood         23.97801               7.882543                     0.392263
 Akaike AIC                 -4.177820             -1.251372                  0.110498
 Schwarz SC              -4.141648               -1.215199                  0.146670
 Mean dependent        0.139246                0.101432                  0.255570
 S.D. dependent           0.027086               0.119725                  0.224231
   
 Determinant resid covariance (dof adj.)            1.78E-07 
 Determinant resid covariance                           1.34E-07 
 Log likelihood                                                     40.22281 
 Akaike information criterion                                 -6.040511 
 Schwarz criterion                                                 -5.787305