If and command

[Dominik Miksch]

Hello,

Can you help me please with my following issue?
I have a panel data set and I want to figure out how ICT adoption influences Labor productivity.
Therefore I can run the simple regression:

LaPr dum_ICT firmage l10 c6 b2b i.a4a i.a1

But I want to make a restriction as I am only interested how ICT adoption influences labor productivity in the 2nd year, if the firm had no ICT adoption in Year 1.
So I created the dummies "dum_ICT" for ICT adoption and "dum_NoICT" if a firm had no ICT adoption.
I tried the following command but it didn't work. Can you help me please, how I can approach that?

  LaPr dum_ICT firmage l10 c6 b2b i.a4a i.a1 if year==2, dum_NoICT(year==1)==0

Kind regards
Dominik

[Richard Williams]

Unless LaPr is itself a command, you have left the command out. Is it xtreg, reg, or what?

Showing the actual output itself will help, Just saying "it doesn't work" is not very informative. Are you getting a syntax error? Does it run but not do what you want? Or what?

I don't know what the code after the comma is for, but I don't think it is legal syntax. Maybe you want an & or a | instead of the comma.

[Dominik Miksch]

Richard Williams Thank you very much for your fast reply. Yes you are right I forgot the command here in that topic.
It was

. reg Inno dum_ICT firmage l10 c6 b2b i.a4a i.a1 if year==2, dum_NoICT(year==1)==0
option dum_NoICT() not allowed
r(198);

Indeed I also don't think that it is the correct syntax. I tried the & as well but it didn't work neither:

. reg Inno dum_ICT firmage l10 c3 b2b i.a4a i.a1 if year==2 & dum_NoICT(year==1)==0
unknown function dum_NoICT()
r(133);

Kind regards
Dominik

[William Lisowski]

Since you have panel data, I will assume that you have a firm identifier I will call firmid, and that dum_ICT takes the value 1 if the firm had ICT adoption in the given year, and 0 if it did not.

xtset firmid year
regress Inno dum_ICT firmage l0 c3 b2b i.a4a i.a1 if year==2 & L.dum_ICT==0

where L.dum_ICT uses the "lag" time series operator, so if year==2 then L.dum_ICT will be the value of dum_ICT in year 1.

See the output of help tsvarlist for more about Stata's time series operators.

[Dominik Miksch]

William Lisowski : Awesome! Thank you very much, that worked perfectly.

. xtset panelid year
       panel variable:  panelid (strongly balanced)
        time variable:  year, 1 to 2
                delta:  1 unit

. regress Inno dum_ICT firmage l10 c3 b2b i.a4a i.a1 if year==2 & L.dum_ICT==0

      Source |       SS           df       MS      Number of obs   =     3,103
-------------+----------------------------------   F(52, 3050)     =     42.74
       Model |  2659.28191        52  51.1400367   Prob > F        =    0.0000
    Residual |  3649.46382     3,050  1.19654552   R-squared       =    0.4215
-------------+----------------------------------   Adj R-squared   =    0.4117
       Total |  6308.74573     3,102  2.03376716   Root MSE        =    1.0939

------------------------------------------------------------------------------
        Inno |      Coef.   Std. Err.      t    P>|t|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
     dum_ICT |   .2845822   .0697638     4.08   0.000     .1477933     .421371
     firmage |  -.0010243   .0015315    -0.67   0.504    -.0040271    .0019784
         l10 |   .5705493   .0458074    12.46   0.000     .4807328    .6603659
          c3 |   .1032498   .0581832     1.77   0.076    -.0108325    .2173322
         b2b |    .000677   .0007668     0.88   0.377    -.0008264    .0021804
             |
         a4a |
          2  |  -.2885407   .2943741    -0.98   0.327    -.8657323    .2886509
          3  |  -.2833497   .3388527    -0.84   0.403    -.9477525    .3810531
          4  |   .0474887    .355741     0.13   0.894    -.6500278    .7450051
          5  |  -.4421766   .2829037    -1.56   0.118    -.9968779    .1125246
          6  |  -.4162328   .2702835    -1.54   0.124    -.9461891    .1137235
          7  |  -.0908338   .3143731    -0.29   0.773    -.7072384    .5255707
          8  |  -.3757523   .2803625    -1.34   0.180    -.9254708    .1739663
          9  |  -.5647735   .2802044    -2.02   0.044    -1.114182    -.015365
         10  |  -.5570642   .4010146    -1.39   0.165     -1.34335     .229222
         11  |   .0529539   .4912183     0.11   0.914    -.9101984    1.016106
         12  |  -.1009795   .3189997    -0.32   0.752    -.7264557    .5244966
         13  |   -.197411   .2702716    -0.73   0.465    -.7273438    .3325219
         14  |  -.6717909   .4492206    -1.50   0.135    -1.552597    .2090148
         15  |  -.1987418   .3154601    -0.63   0.529    -.8172777    .4197941
         16  |    .290117   .3185079     0.91   0.362    -.3343948    .9146287
         17  |   -1.44027   .8197693    -1.76   0.079    -3.047626    .1670859
         18  |   .5777043   .8202959     0.70   0.481    -1.030684    2.186093
         19  |  -.3818752   .2680905    -1.42   0.154    -.9075315    .1437811
         20  |  -.2772761   .2735206    -1.01   0.311    -.8135795    .2590272
         21  |  -.6216942   .3072893    -2.02   0.043    -1.224209   -.0191792
         23  |  -.4837853   .3432089    -1.41   0.159    -1.156729     .189159
         24  |  -.4641845   .2853611    -1.63   0.104    -1.023704     .095335
         25  |   -.971511   .3362687    -2.89   0.004    -1.630847   -.3121749
             |
          a1 |
         11  |   .1634681   .1675756     0.98   0.329    -.1651045    .4920408
         12  |  -.3999711   .1618933    -2.47   0.014     -.717402   -.0825401
         13  |  -.1681401   .2141821    -0.79   0.432     -.588096    .2518158
         14  |  -.2134868   .2321303    -0.92   0.358    -.6686344    .2416608
         15  |   .3120863   .1438212     2.17   0.030       .03009    .5940826
         16  |  -.2574673   .1790772    -1.44   0.151    -.6085916     .093657
         17  |  -.1769258   .1475234    -1.20   0.231    -.4661812    .1123295
         18  |   .4848021   .1341442     3.61   0.000       .22178    .7478242
         19  |   1.083772   .1396287     7.76   0.000     .8099967    1.357548
         20  |   1.801743   .2438499     7.39   0.000     1.323616     2.27987
         21  |   1.915563     .14788    12.95   0.000     1.625609    2.205518
         22  |  -.0225719   .1868979    -0.12   0.904    -.3890305    .3438867
         23  |   1.349221   .1709095     7.89   0.000     1.014112    1.684331
         25  |  -.0714195   .1505803    -0.47   0.635    -.3666687    .2238297
         27  |   1.790655   .1183697    15.13   0.000     1.558562    2.022747
         28  |   1.999689   .1823233    10.97   0.000       1.6422    2.357178
         29  |   .9985773   .1282099     7.79   0.000     .7471907    1.249964
         30  |   .6118559   .1740438     3.52   0.000     .2706009     .953111
         31  |  -.4342055   .1394508    -3.11   0.002    -.7076325   -.1607785
         32  |   2.301774   .1525156    15.09   0.000      2.00273    2.600817
         33  |   .7592134   .2025517     3.75   0.000     .3620618    1.156365
         34  |   1.854734   .1338328    13.86   0.000     1.592322    2.117146
         35  |   1.692545   .1409749    12.01   0.000      1.41613    1.968961
         36  |   .7192039   .1578082     4.56   0.000     .4097826    1.028625
             |
       _cons |   .2699117    .281987     0.96   0.339     -.282992    .8228155
------------------------------------------------------------------------------

[William Lisowski]

Thank you for closing the loop.

Looking at your regreesion, I realize I should have suggested you replace your independent variable dum_ICT with i.dum_ICT. It won't make a difference to your regression results, but should you eventually discover and utilize some of Stata's postestimation commands (e.g., as described by help regress postestimaton) those commands will understand where necessary that an indicator variable cannot be changed by an incremental amount but instead by an entire unit, from 0 to 1 or 1 to 0.

And if dum_ICT was based on a categorical variable, say ICT that took values 1 for ICT use and and 2 for no ICT use, respectively, you could instead substitute ib2.ICT, avoiding the dummy variable entirely.