面板数据使用LLC方法进行单位根检验，进行差分后再检验就是平稳的意思吗？ 如何看单位根检验的结果
检验结果如下：
xtunitroot llc lnpfi
Levin-Lin-Chu unit-root test for lnpfi
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Ho: Panels contain unit roots               Number of panels  =     31
Ha: Panels are stationary                   Number of periods =     15
AR parameter: Common                        Asymptotics: N/T -> 0
Panel means:  Included
Time trend:   Not included
ADF regressions: 1 lag
LR variance:     Bartlett kernel, 7.00 lags average (chosen by LLC)
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                    Statistic      p-value
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Unadjusted t        -2.0356
Adjusted t*         -0.1518        0.4397
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. xtunitroot llc D.lnpfi
Levin-Lin-Chu unit-root test for D.lnpfi
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Ho: Panels contain unit roots               Number of panels  =     31
Ha: Panels are stationary                   Number of periods =     14
AR parameter: Common                        Asymptotics: N/T -> 0
Panel means:  Included
Time trend:   Not included
ADF regressions: 1 lag
LR variance:     Bartlett kernel, 7.00 lags average (chosen by LLC)
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                    Statistic      p-value
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Unadjusted t       -15.4607
Adjusted t*         -8.1944        0.0000
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