Dear Stata users,
I need your point of view about this subject. I run a xtlogit regression with the following code
Code:
  xtlogit a001 l2.a016 l2.a017 l2.a020_new l2.i.Cooperation_i l2.i.Patents l2.i.Formal_protection l2.i.Uncertainty_1 l2.i.Lack_of_demand_1 l2.i.a023 l2.i.a019 l2.i.a018 l2.a041_l2_imput i.anyo if KIBS==1, nolog i(ident)
And the output is:
Code:
 Random-effects logistic regression              Number of obs     =      5,291
Group variable: ident                           Number of groups  =      1,132

Random effects u_i ~ Gaussian                   Obs per group:
                                                              min =          1
                                                              avg =        4.7
                                                              max =          7

Integration method: mvaghermite                 Integration pts.  =         12

                                                Wald chi2(18)     =     253.45
Log likelihood  = -1973.5183                    Prob > chi2       =     0.0000

--------------------------------------------------------------------------------------
                a001 |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
---------------------+----------------------------------------------------------------
                a016 |
                 L2. |   1.259905   .5905704     2.13   0.033     .1024086    2.417402
                     |
                a017 |
                 L2. |  -.6262536   .1702988    -3.68   0.000    -.9600332    -.292474
                     |
            a020_new |
                 L2. |    .568769   .0815715     6.97   0.000     .4088919    .7286461
                     |
    L2.Cooperation_i |
                  1  |   1.113954   .1598741     6.97   0.000     .8006067    1.427302
                     |
          L2.Patents |
                  1  |   .7914137     .24456     3.24   0.001     .3120848    1.270743
                     |
L2.Formal_protection |
                  1  |   .3822348   .1641714     2.33   0.020     .0604647    .7040048
                     |
    L2.Uncertainty_1 |
                  1  |  -.0765705   .1571487    -0.49   0.626    -.3845763    .2314353
                     |
 L2.Lack_of_demand_1 |
                  1  |  -.8825044   .3400314    -2.60   0.009    -1.548954    -.216055
                     |
             L2.a023 |
                  1  |   .0715742   .1784459     0.40   0.688    -.2781734    .4213218
                     |
             L2.a019 |
                  1  |   .7478324    .154126     4.85   0.000     .4457509    1.049914
                     |
             L2.a018 |
                  1  |  -.4510715   .2307392    -1.95   0.051     -.903312     .001169
                     |
       a041_l2_imput |
                 L2. |     .05995   .0655042     0.92   0.360    -.0684358    .1883358
                     |
                anyo |
               2007  |  -.1587466    .300931    -0.53   0.598    -.7485606    .4310674
               2008  |  -.5519556    .326635    -1.69   0.091    -1.192148    .0882373
               2009  |  -.8064692   .3364888    -2.40   0.017    -1.465975   -.1469632
               2010  |  -.8347762   .3226738    -2.59   0.010    -1.467205   -.2023471
               2011  |  -.9288709   .3251345    -2.86   0.004    -1.566123   -.2916189
               2012  |   -.894516    .326696    -2.74   0.006    -1.534828   -.2542036
                     |
               _cons |   3.227972   .7576384     4.26   0.000     1.743028    4.712916
---------------------+----------------------------------------------------------------
            /lnsig2u |   2.549213   .1175276                      2.318863    2.779563
---------------------+----------------------------------------------------------------
             sigma_u |   3.577293   .2102154                       3.18812    4.013972
                 rho |   .7954939   .0191198                      .7554724    .8304352
--------------------------------------------------------------------------------------
LR test of rho=0: chibar2(01) = 1270.48                Prob >= chibar2 = 0.000
We can see how the variables a016 (with 2 lags) is significant (p=0.06). However, when I run the regression year by year instead of the panel, this variable is not significant in any year, why? At least in a year it should be significant, shouldn't it?
Code:
. . logit a001 l2.a016 l2.a017 l2.a020_new l2.Cooperation_i l2.Patents l2.Formal_protection l2.Uncertainty_1  l2.Lack_of_demand_1 l2.a023 l2.a019 l2.a018 l2.a041_l2_imput if KIBS==1 & anyo==2006 , nolog vce(robust)
note: L2.a041_l2_imput omitted because of collinearity

Logistic regression                             Number of obs     =        622
                                                Wald chi2(11)     =      98.63
                                                Prob > chi2       =     0.0000
Log pseudolikelihood = -299.34763               Pseudo R2         =     0.1961

-----------------------------------------------------------------------------------
                  |               Robust
             a001 |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
------------------+----------------------------------------------------------------
             a016 |
              L2. |  -.1112366   .7128861    -0.16   0.876    -1.508468    1.285995
                  |
             a017 |
              L2. |  -.1826609   .1747374    -1.05   0.296    -.5251399    .1598181
                  |
         a020_new |
              L2. |   .3366679    .111882     3.01   0.003     .1173832    .5559526
                  |
    Cooperation_i |
              L2. |   .9712777   .2326144     4.18   0.000     .5153618    1.427194
                  |
          Patents |
              L2. |   .7099016   .3366658     2.11   0.035     .0500488    1.369754
                  |
Formal_protection |
              L2. |   .5488279   .2504874     2.19   0.028     .0578816    1.039774
                  |
    Uncertainty_1 |
              L2. |  -.6255862    .253396    -2.47   0.014    -1.122233   -.1289391
                  |
 Lack_of_demand_1 |
              L2. |  -.5590903   .3561561    -1.57   0.116    -1.257143    .1389628
                  |
             a023 |
              L2. |   .3175696   .2277358     1.39   0.163    -.1287843    .7639235
                  |
             a019 |
              L2. |   1.099278   .2124885     5.17   0.000     .6828082    1.515748
                  |
             a018 |
              L2. |  -.3316308   .2496165    -1.33   0.184    -.8208702    .1576086
                  |
    a041_l2_imput |
              L2. |          0  (omitted)
                  |
            _cons |    1.68028    1.05047     1.60   0.110    -.3786031    3.739163
-----------------------------------------------------------------------------------

. . outreg2 using EVOLUTION.xls, replace ctitle(Coeff 2006) label long
EVOLUTION.xls
dir : seeout

. . logit a001 l2.a016 l2.a017 l2.a020_new l2.Cooperation_i l2.Patents l2.Formal_protection l2.Uncertainty_1  l2.Lack_of_demand_1 l2.a023 l2.a019 l2.a018 l2.a041_l2_imput if KIBS==1 & anyo==2007 , nolog vce(robust)

Logistic regression                             Number of obs     =        849
                                                Wald chi2(12)     =     153.37
                                                Prob > chi2       =     0.0000
Log pseudolikelihood = -415.92454               Pseudo R2         =     0.1889

-----------------------------------------------------------------------------------
                  |               Robust
             a001 |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
------------------+----------------------------------------------------------------
             a016 |
              L2. |  -.2131488   .5382453    -0.40   0.692     -1.26809    .8417927
                  |
             a017 |
              L2. |  -.1423844   .1533541    -0.93   0.353    -.4429529    .1581841
                  |
         a020_new |
              L2. |    .271747    .094453     2.88   0.004     .0866226    .4568715
                  |
    Cooperation_i |
              L2. |   .9360836   .2058198     4.55   0.000     .5326843    1.339483
                  |
          Patents |
              L2. |   .7979549   .3241309     2.46   0.014       .16267     1.43324
                  |
Formal_protection |
              L2. |   .3478325   .2026556     1.72   0.086    -.0493652    .7450301
                  |
    Uncertainty_1 |
              L2. |  -.1051461   .2141874    -0.49   0.623    -.5249456    .3146534
                  |
 Lack_of_demand_1 |
              L2. |  -.9149895   .4676112    -1.96   0.050    -1.831491    .0015115
                  |
             a023 |
              L2. |   .5581436   .2042502     2.73   0.006     .1578206    .9584665
                  |
             a019 |
              L2. |   .6301086   .1901807     3.31   0.001     .2573613    1.002856
                  |
             a018 |
              L2. |  -.2777743   .2120486    -1.31   0.190    -.6933819    .1378333
                  |
    a041_l2_imput |
              L2. |   .6324045   .1150863     5.50   0.000     .4068396    .8579695
                  |
            _cons |  -.4679732    .911222    -0.51   0.608    -2.253936    1.317989
-----------------------------------------------------------------------------------

. . outreg2 using EVOLUTION.xls, append ctitle(Coeff 2007) label long
EVOLUTION.xls
dir : seeout

. . logit a001 l2.a016 l2.a017 l2.a020_new l2.Cooperation_i l2.Patents l2.Formal_protection l2.Uncertainty_1  l2.Lack_of_demand_1 l2.a023 l2.a019 l2.a018 l2.a041_l2_imput if KIBS==1 & anyo==2008 , nolog vce(robust)
note: L2.a023 omitted because of collinearity

Logistic regression                             Number of obs     =        858
                                                Wald chi2(11)     =     169.36
                                                Prob > chi2       =     0.0000
Log pseudolikelihood = -421.62556               Pseudo R2         =     0.2198

-----------------------------------------------------------------------------------
                  |               Robust
             a001 |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
------------------+----------------------------------------------------------------
             a016 |
              L2. |   .2012109   .5021558     0.40   0.689    -.7829963    1.185418
                  |
             a017 |
              L2. |  -.2305827   .1392882    -1.66   0.098    -.5035826    .0424172
                  |
         a020_new |
              L2. |   .3378666    .080816     4.18   0.000       .17947    .4962631
                  |
    Cooperation_i |
              L2. |   1.076619   .2080259     5.18   0.000     .6688957    1.484342
                  |
          Patents |
              L2. |   .3903703   .3263694     1.20   0.232    -.2493019    1.030042
                  |
Formal_protection |
              L2. |    .771911   .2159984     3.57   0.000     .3485619     1.19526
                  |
    Uncertainty_1 |
              L2. |   -.310516   .1982328    -1.57   0.117    -.6990452    .0780132
                  |
 Lack_of_demand_1 |
              L2. |  -.3306299   .4372156    -0.76   0.450    -1.187557    .5262969
                  |
             a023 |
              L2. |          0  (omitted)
                  |
             a019 |
              L2. |   .8938054   .1816854     4.92   0.000     .5377086    1.249902
                  |
             a018 |
              L2. |  -.2981233   .2014168    -1.48   0.139    -.6928931    .0966464
                  |
    a041_l2_imput |
              L2. |   .4350123   .0974972     4.46   0.000     .2439212    .6261033
                  |
            _cons |   -.359421   .7880703    -0.46   0.648     -1.90401    1.185168
-----------------------------------------------------------------------------------

. . outreg2 using EVOLUTION.xls, append ctitle(Coeff 2008) label long
EVOLUTION.xls
dir : seeout

. . logit a001 l2.a016 l2.a017 l2.a020_new l2.Cooperation_i l2.Patents l2.Formal_protection l2.Uncertainty_1  l2.Lack_of_demand_1 l2.a023 l2.a019 l2.a018 l2.a041_l2_imput if KIBS==1 & anyo==2009 , nolog vce(robust)
note: L2.a023 omitted because of collinearity

Logistic regression                             Number of obs     =        756
                                                Wald chi2(11)     =     166.93
                                                Prob > chi2       =     0.0000
Log pseudolikelihood = -368.57698               Pseudo R2         =     0.2362

-----------------------------------------------------------------------------------
                  |               Robust
             a001 |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
------------------+----------------------------------------------------------------
             a016 |
              L2. |  -.9807419   .5967298    -1.64   0.100    -2.150311     .188827
                  |
             a017 |
              L2. |   -.044206   .1611352    -0.27   0.784    -.3600251    .2716131
                  |
         a020_new |
              L2. |   .5807934   .1077796     5.39   0.000     .3695493    .7920376
                  |
    Cooperation_i |
              L2. |   1.043581   .2214448     4.71   0.000     .6095571    1.477605
                  |
          Patents |
              L2. |   .2375545   .3195208     0.74   0.457    -.3886947    .8638038
                  |
Formal_protection |
              L2. |   .4818765   .2320089     2.08   0.038     .0271475    .9366055
                  |
    Uncertainty_1 |
              L2. |  -.1946339   .2192723    -0.89   0.375    -.6243997    .2351319
                  |
 Lack_of_demand_1 |
              L2. |  -.4896681   .5697698    -0.86   0.390    -1.606396    .6270602
                  |
             a023 |
              L2. |          0  (omitted)
                  |
             a019 |
              L2. |   1.022031   .2042504     5.00   0.000     .6217072    1.422354
                  |
             a018 |
              L2. |  -.0132281    .222954    -0.06   0.953    -.4502098    .4237537
                  |
    a041_l2_imput |
              L2. |   .3620461   .1014231     3.57   0.000     .1632604    .5608318
                  |
            _cons |   1.992083   .9781928     2.04   0.042     .0748608    3.909306
-----------------------------------------------------------------------------------

. . outreg2 using EVOLUTION.xls, append ctitle(Coeff 2009) label long
EVOLUTION.xls
dir : seeout

. . logit a001 l2.a016 l2.a017 l2.a020_new l2.Cooperation_i l2.Patents l2.Formal_protection l2.Uncertainty_1  l2.Lack_of_demand_1 l2.a023 l2.a019 l2.a018 l2.a041_l2_imput if KIBS==1 & anyo==2010 , nolog vce(robust)

Logistic regression                             Number of obs     =        737
                                                Wald chi2(12)     =     196.00
                                                Prob > chi2       =     0.0000
Log pseudolikelihood = -344.01382               Pseudo R2         =     0.2670

-----------------------------------------------------------------------------------
                  |               Robust
             a001 |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
------------------+----------------------------------------------------------------
             a016 |
              L2. |  -.1034403    .561866    -0.18   0.854    -1.204677    .9977969
                  |
             a017 |
              L2. |  -.2056485   .1362254    -1.51   0.131    -.4726454    .0613484
                  |
         a020_new |
              L2. |   .4356376   .1085408     4.01   0.000     .2229015    .6483737
                  |
    Cooperation_i |
              L2. |   1.204631   .2278846     5.29   0.000     .7579853    1.651277
                  |
          Patents |
              L2. |   1.136678   .3898595     2.92   0.004     .3725671    1.900788
                  |
Formal_protection |
              L2. |   .3959672   .2525748     1.57   0.117    -.0990703    .8910047
                  |
    Uncertainty_1 |
              L2. |  -.3183775   .2300575    -1.38   0.166    -.7692819    .1325269
                  |
 Lack_of_demand_1 |
              L2. |  -.6298557    .432337    -1.46   0.145    -1.477221    .2175093
                  |
             a023 |
              L2. |   .2793232   .2246197     1.24   0.214    -.1609232    .7195696
                  |
             a019 |
              L2. |   1.258281   .2069898     6.08   0.000      .852588    1.663973
                  |
             a018 |
              L2. |  -.2595075   .2348023    -1.11   0.269    -.7197114    .2006965
                  |
    a041_l2_imput |
              L2. |   .0141612   .0654346     0.22   0.829    -.1140883    .1424107
                  |
            _cons |   1.809871   .9399449     1.93   0.054    -.0323868    3.652129
-----------------------------------------------------------------------------------

. . outreg2 using EVOLUTION.xls, append ctitle(Coeff 2010) label long
EVOLUTION.xls
dir : seeout

. . logit a001 l2.a016 l2.a017 l2.a020_new l2.Cooperation_i l2.Patents l2.Formal_protection l2.Uncertainty_1  l2.Lack_of_demand_1 l2.a023 l2.a019 l2.a018 l2.a041_l2_imput if KIBS==1 & anyo==2011 , nolog vce(robust)

Logistic regression                             Number of obs     =        741
                                                Wald chi2(12)     =     176.74
                                                Prob > chi2       =     0.0000
Log pseudolikelihood = -363.59203               Pseudo R2         =     0.2428

-----------------------------------------------------------------------------------
                  |               Robust
             a001 |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
------------------+----------------------------------------------------------------
             a016 |
              L2. |  -.0690211   .4919949    -0.14   0.888    -1.033313    .8952711
                  |
             a017 |
              L2. |  -.2527411   .1226367    -2.06   0.039    -.4931047   -.0123775
                  |
         a020_new |
              L2. |   .4470355   .0947164     4.72   0.000     .2613948    .6326762
                  |
    Cooperation_i |
              L2. |   .5992232   .2212969     2.71   0.007     .1654892    1.032957
                  |
          Patents |
              L2. |    .822962   .3363063     2.45   0.014     .1638137     1.48211
                  |
Formal_protection |
              L2. |   .1968315   .2370152     0.83   0.406    -.2677097    .6613727
                  |
    Uncertainty_1 |
              L2. |  -.3404033     .20806    -1.64   0.102    -.7481934    .0673869
                  |
 Lack_of_demand_1 |
              L2. |  -.9143127   .4489594    -2.04   0.042    -1.794257   -.0343686
                  |
             a023 |
              L2. |   .3892406   .2134405     1.82   0.068    -.0290952    .8075764
                  |
             a019 |
              L2. |   1.421359    .210311     6.76   0.000     1.009157    1.833561
                  |
             a018 |
              L2. |   -.179748    .210217    -0.86   0.393    -.5917658    .2322698
                  |
    a041_l2_imput |
              L2. |   .0699654   .0694212     1.01   0.314    -.0660976    .2060283
                  |
            _cons |   1.827838   .8373989     2.18   0.029     .1865661     3.46911
-----------------------------------------------------------------------------------

. . outreg2 using EVOLUTION.xls, append ctitle(Coeff 2011) label long
EVOLUTION.xls
dir : seeout

. . logit a001 l2.a016 l2.a017 l2.a020_new l2.Cooperation_i l2.Patents l2.Formal_protection l2.Uncertainty_1  l2.Lack_of_demand_1 l2.a023 l2.a019 l2.a018 l2.a041_l2_imput if KIBS==1 & anyo==2012 , nolog vce(robust)

Logistic regression                             Number of obs     =        728
                                                Wald chi2(12)     =     167.01
                                                Prob > chi2       =     0.0000
Log pseudolikelihood = -354.92664               Pseudo R2         =     0.2431

-----------------------------------------------------------------------------------
                  |               Robust
             a001 |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
------------------+----------------------------------------------------------------
             a016 |
              L2. |   .0494455   .5085783     0.10   0.923    -.9473496    1.046241
                  |
             a017 |
              L2. |  -.2832533   .1255205    -2.26   0.024     -.529269   -.0372376
                  |
         a020_new |
              L2. |   .3940466   .1038325     3.80   0.000     .1905387    .5975545
                  |
    Cooperation_i |
              L2. |    1.05619   .2170891     4.87   0.000     .6307034    1.481677
                  |
          Patents |
              L2. |    1.16947   .4051364     2.89   0.004     .3754171    1.963523
                  |
Formal_protection |
              L2. |    .400208   .2541834     1.57   0.115    -.0979824    .8983983
                  |
    Uncertainty_1 |
              L2. |  -.1346875   .2083407    -0.65   0.518    -.5430279    .2736528
                  |
 Lack_of_demand_1 |
              L2. |   .1489476   .5305875     0.28   0.779    -.8909848     1.18888
                  |
             a023 |
              L2. |   .2460763   .2080506     1.18   0.237    -.1616953    .6538478
                  |
             a019 |
              L2. |   1.082133   .2151312     5.03   0.000     .6604835    1.503782
                  |
             a018 |
              L2. |  -.1220714   .2173202    -0.56   0.574    -.5480111    .3038684
                  |
    a041_l2_imput |
              L2. |   .1477079    .068884     2.14   0.032     .0126977    .2827181
                  |
            _cons |    1.16257   .8887304     1.31   0.191      -.57931    2.904449
-----------------------------------------------------------------------------------

. . outreg2 using EVOLUTION.xls, append ctitle(Coeff 2012) label long
EVOLUTION.xls
dir : seeout

.
end of do-file

. do "C:\Users\ragucar\AppData\Local\Temp\STD04000000.tmp"

. . logit a001 l2.a016 l2.a017 l2.a020_new l2.i.Cooperation_i l2.i.Patents l2.i.Formal_protection l2.i.Uncertainty_1 l2.i.Lack_of_demand_1 l2.i.a023 l2.i.a019 l2.i.a018 l2.a041_l2_imput if KIBS==1 & anyo==2006 , nolog vce(robust)
note: L2.a041_l2_imput omitted because of collinearity

Logistic regression                             Number of obs     =        622
                                                Wald chi2(11)     =      98.63
                                                Prob > chi2       =     0.0000
Log pseudolikelihood = -299.34763               Pseudo R2         =     0.1961

--------------------------------------------------------------------------------------
                     |               Robust
                a001 |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
---------------------+----------------------------------------------------------------
                a016 |
                 L2. |  -.1112366   .7128861    -0.16   0.876    -1.508468    1.285995
                     |
                a017 |
                 L2. |  -.1826609   .1747374    -1.05   0.296    -.5251399    .1598181
                     |
            a020_new |
                 L2. |   .3366679    .111882     3.01   0.003     .1173832    .5559526
                     |
    L2.Cooperation_i |
                  1  |   .9712777   .2326144     4.18   0.000     .5153618    1.427194
                     |
          L2.Patents |
                  1  |   .7099016   .3366658     2.11   0.035     .0500488    1.369754
                     |
L2.Formal_protection |
                  1  |   .5488279   .2504874     2.19   0.028     .0578816    1.039774
                     |
    L2.Uncertainty_1 |
                  1  |  -.6255862    .253396    -2.47   0.014    -1.122233   -.1289391
                     |
 L2.Lack_of_demand_1 |
                  1  |  -.5590903   .3561561    -1.57   0.116    -1.257143    .1389628
                     |
             L2.a023 |
                  1  |   .3175696   .2277358     1.39   0.163    -.1287843    .7639235
                     |
             L2.a019 |
                  1  |   1.099278   .2124885     5.17   0.000     .6828082    1.515748
                     |
             L2.a018 |
                  1  |  -.3316308   .2496165    -1.33   0.184    -.8208702    .1576086
                     |
       a041_l2_imput |
                 L2. |          0  (omitted)
                     |
               _cons |    1.68028    1.05047     1.60   0.110    -.3786031    3.739163
--------------------------------------------------------------------------------------
Thanks for your help!
Rocio