我用的是面板数据，用的是STATA9.0，采用B-C1992年模型，命令是
xtfrontier  L realout mach fe ca sown irri  draught  northeast northwest middle southwest southeast south, tvd cost
迭代过程如下：

Iteration	0:	log	likelihood	=	129.20827	(not	concave)
Iteration	1:	log	likelihood	=	156.85453	(not	concave)
Iteration	2:	log	likelihood	=	217.86963
Iteration	3:	log	likelihood	=	294.9994
Iteration	4:	log	likelihood	=	322.94202
Iteration	5:	log	likelihood	=	326.57645
Iteration	6:	log	likelihood	=	334.46053
Iteration	7:	log	likelihood	=	335.18159
Iteration	8:	log	likelihood	=	335.39737
Iteration	9:	log	likelihood	=	335.5494
Iteration	10:	log	likelihood	=	335.61286
Iteration	11:	log	likelihood	=	335.65008
Iteration	12:	log	likelihood	=	335.68119
Iteration	13:	log	likelihood	=	335.68708
Iteration	14:	log	likelihood	=	335.69465
Iteration	15:	log	likelihood	=	335.69553
Iteration	16:	log	likelihood	=	335.69801
Iteration	17:	log	likelihood	=	335.69834
Iteration	18:	log	likelihood	=	335.69882
Iteration	19:	log	likelihood	=	335.69889
Iteration	20:	log	likelihood	=	335.69891

输出结果如下：

Wald chi2(13)	= 4281.56
Log likelihood	= 335.69891	Prob >	chi2 =	0.0000
L	Coef. Std. Err.	z	P>z	[95% Conf.	Interval]
realout	-.1062835 .0464414	-2.29	0.022	-.1973071	-.01526
mach	-.0394763 .0184491	-2.14	0.032	-.0756359	-.0033167
fe	.1150766 .0443276	2.60	0.009	.028196	.2019572
ca	.0135131 .1036557	0.13	0.896	-.1896483	.2166746
sown	.3718729 .0723463	5.14	0.000	.2300767	.5136691
irri	.1719977 .0568807	3.02	0.002	.0605135	.2834818
draught	.0459225 .0170264	2.70	0.007	.0125515	.0792936
northeast	-.3377804 .0832586	-4.06	0.000	-.5009642	-.1745965
northwest	-.8143119 .0847163	-9.61	0.000	-.9803528	-.6482709
middle	.2088442 .0739921	2.82	0.005	.0638224	.353866
southwest	.7233478 .0605002	11.96	0.000	.6047697	.841926
southeast	.3691173 .0816535	4.52	0.000	.2090794	.5291552
south	-.3284567 .1551188	-2.12	0.034	-.632484	-.0244294
_cons	2.036215 .6273906	3.25	0.001	.8065515	3.265878
/mu	-6.450609 34.47498	-0.19	0.852	-74.02032	61.1191
/eta	-.0053492 .0031916	-1.68	0.094	-.0116046	.0009062
/lnsigma2	.9635782 4.82056	0.20	0.842	-8.484546	10.4117
/ilgtgamma	6.826027 4.828011	1.41	0.157	-2.636701	16.28875
sigma2	2.621058 12.63497		.0002066	33246.43
gamma	.998916 .0052278		.0668134	.9999999
sigma_u2	2.618217 12.63497		-22.14588	27.38231
sigma_v2	.0028412 .0002573		.0023369	.0033455

我想请教大家几个问题，第一，系数检验给出的是Z值，而不是t值，两者是作用是一样的吗？比如第一个变量realout的系数在1%的统计水平上显著，可以这么说吗？
第二，回归结果第二组的最后一个/ilgtgamma代表什么意思呢？
第三，B-C1995模型可以用STATA来估计吗？
求教各位解惑，不甚感激！