I’m conducting a DID estimation by applying Callaway & Sant'Anna (2021). I have a firm-level panel and estimate the impact of a policy change on product innovation. Different firms got treatment in different years and many other firms are not subject to this policy change and they got never treated. Several thousands of firms got treated and lakhs of firms did not get treatment.
My data is an un-balance panel from 2000 to 2016. Firms got treatment from 2001 to 2010. But once the firm got treated it is considered as treated for the subsequent years.
My outcome variable is product_new which is a dummy taking the value 1 or 0, depending on if the firm has introduced a new product or not.
I use the following co-variates
sales_million_inr
wages_million_inr
log_age
plant_size
staff_welfare_million_inr
cash_holding_million_inr
my DID command is as follows
first treat – refers to the year firm got treatment for the first time and 0 for the never treated firms
nic_2_digit is the sector that firm belongs to
Data sample is given below
The results are given as follows
[/CODE]
This command provides the post estimation results
1) I understand that here parallel trend is not satisfied . Can adding more co-variates help in ensuring the parallel trend? Once I try with more covariates (including dummy variables), much of the treatment effects in the long table I gave above gets omitted. What would be the reason and is thee any way to rectify this ?
2) My second question is that if firms are anticipating a policy change make changes in the product portfolio before the policy gets implemented, can we take care of such an anticipatory effect in the did equation ?
Thank you so much in advance
My data is an un-balance panel from 2000 to 2016. Firms got treatment from 2001 to 2010. But once the firm got treated it is considered as treated for the subsequent years.
My outcome variable is product_new which is a dummy taking the value 1 or 0, depending on if the firm has introduced a new product or not.
I use the following co-variates
sales_million_inr
wages_million_inr
log_age
plant_size
staff_welfare_million_inr
cash_holding_million_inr
my DID command is as follows
Code:
csdid product_new sales_million_inr wages_million_inr log_age plant_size staff_welfare_million_inr cash_holding_million_inr, ivar(fact_id) time(year) gvar(first_treat) custer(nic_2_digit)
first treat – refers to the year firm got treatment for the first time and 0 for the never treated firms
nic_2_digit is the sector that firm belongs to
Data sample is given below
Code:
* Example generated by -dataex-. For more info, type help dataex clear input float(fact_id year first_treat) byte nic_2_digit float(product_new sales_million_inr wages_million_inr log_age plant_size staff_welfare_million_inr cash_holding_million_inr) 1 2000 0 18 0 3.68349 .47554 .60206 1.1139433 .007944 .681019 1 2002 0 17 0 2.649905 .232361 .7781513 .60206 0 .087527 1 2004 0 17 0 . .036 .90309 0 0 .196293 1 2007 0 17 0 . . . . . . 2 2008 0 34 0 . . . . . . 2 2010 0 29 0 9.33479 1.538032 1.146128 1.146128 .021024 .395556 3 2006 0 28 0 . . . . . . 3 2008 0 28 0 . . . . . . 4 2011 0 23 0 . . . . 0 . 4 2013 0 23 0 . . .4771213 . 0 . 4 2014 0 23 0 . . .60206 . 0 . 4 2016 0 23 0 . . .7781513 . 0 . 5 2011 0 27 0 . .249611 1.20412 .60206 .086878 11.108895 6 2000 0 26 0 1.796932 .323573 1.0791812 1.0413927 .025503 .077545 6 2001 0 26 0 1.112399 .277877 1.20412 1.1139433 .013907 .038135 6 2002 0 26 0 2.66122 .294578 1.50515 .9542425 .035365 .040831 6 2005 2007 26 0 3.89348 .45639 1.544068 1.230449 .027381 .288438 6 2010 2007 23 1 7.270035 1.011868 1.60206 1.3424227 .295312 .208866 7 2000 0 17 0 5.384419 .454524 .4771213 1.230449 0 .0156 7 2003 2005 17 0 5.204181 .583106 .7781513 1.1139433 0 .090684 7 2004 2005 17 1 5.556683 .579233 .90309 1.2787536 0 .044252 8 2007 0 34 0 14.676222 1.770737 .30103 1.361728 .000828 .244657 8 2014 0 29 1 49.7901 3.733146 .9542425 1.462398 .198382 .120608 8 2015 0 29 0 30.25556 4.492578 1 1.518514 .115234 2.75696 9 2006 0 16 0 .3054 .198063 .90309 1.1760913 0 .079132 10 2016 0 19 0 . . . . 0 . 11 2000 0 22 0 12.892373 .733892 1.20412 1.1139433 .044168 .002133 11 2005 2003 21 0 22.01284 1.021435 .7781513 1.2787536 .141496 .18434 11 2015 0 17 0 . . . . 0 . 12 2003 0 26 0 2.553519 .370875 1.3222193 1.230449 .041361 .181588 12 2009 0 23 1 2.175183 .887775 1.4771212 1 .005768 .0864 12 2010 0 23 0 2.365626 .757608 1.4913617 .90309 .006112 .063911 12 2015 0 23 0 5.614366 .435722 1.518514 .845098 .010756 .408777 13 2006 0 18 0 . . . . . . 13 2008 0 18 0 . . . . . . 14 2007 2007 33 0 19.10748 3.647095 .4771213 1.929419 .162801 .004973 14 2008 0 24 1 33.497414 7.441445 .69897 2.2227166 .00299 .46184 14 2009 0 32 1 32.53304 8.020466 .7781513 2.10721 .050507 .490319 14 2010 0 32 1 47.80494 7.246658 .845098 1.995635 .049732 .372375 14 2011 0 32 0 63.42744 6.688226 .90309 1.9542425 .13571 .428162 14 2013 0 32 1 115.24628 13.975908 1 1.60206 .408584 .205459 14 2014 0 32 0 199.1004 17.117374 1.0413927 2.0934217 .238519 2.676359 14 2015 0 32 0 197.04155 25.662535 1.0791812 2.2253094 .781237 .663783 14 2016 0 32 1 212.3099 35.334366 1.1139433 2.2944663 .49422 2.61468 15 2006 0 16 0 5.242968 2.212626 1.4771212 1.94939 0 .099987 15 2007 0 16 0 10.33662 4.291706 1.4913617 2.4133 0 .304321 15 2008 0 16 0 11.344304 4.162863 1.50515 2.38739 .055 .223694 16 2003 2007 28 0 9.20535 .399885 1.230449 1.2552725 0 .157427 16 2005 2007 28 0 9.034805 .50022 1.2787536 1.1760913 0 .122201 16 2013 0 25 1 13.6353 .81421 1.4313638 1.30103 .010255 .554098 17 2004 0 24 0 22.34008 5.535244 1.230449 2.1583624 .147385 .034567 18 2014 0 24 0 717.8102 3.554736 .30103 1.60206 0 40.21732 18 2015 0 24 0 523.89417 5.433266 1.0791812 1.838849 0 56.79501 19 2007 0 22 0 . . . . . . 19 2013 0 18 0 . . . . 0 . 20 2005 0 26 0 6.332628 .210993 1.447158 1.0791812 .00216 .314208 20 2009 2006 23 1 8.207835 .173617 1.4149734 .7781513 .007531 .226525 20 2011 2007 23 1 3.81726 .276232 1.531479 .90309 .004001 .182846 21 2004 0 18 0 . . . . . . 22 2007 2006 24 0 50.14235 .877559 .7781513 1.1139433 .024216 .103025 22 2008 2006 24 0 53.86041 1.233524 .845098 1.146128 .026285 3.024251 22 2014 0 20 1 153.539 3.704187 1.20412 1.146128 .055697 6.97758 23 2007 0 16 0 .118635 .05777 1.447158 .7781513 0 .000225 24 2004 0 24 0 15.0476 .754575 1.146128 1.1760913 .001397 .580133 24 2005 0 24 1 18.266556 .907704 1.1760913 1.20412 .002708 2.236578 24 2011 0 21 0 . . . . 0 . 25 2010 0 25 0 . . . . 0 . 26 2001 0 29 0 . . . . . . 26 2004 0 29 0 . . . . . . 27 2006 0 26 0 .323488 .130626 1.39794 .69897 .00207 .054032 27 2011 0 23 1 11.530116 2.314494 1.612784 1.724276 .207932 .915701 27 2013 0 23 1 .63905 .31937 1.7075702 .9542425 .005953 .043355 28 2001 0 20 0 . . . . . . 29 2007 0 25 0 8.689664 .665788 .7781513 1.1139433 .009677 .233638 29 2008 2008 25 1 11.51524 .928 .845098 1.2787536 .002418 .171861 30 2006 0 16 0 5.242968 2.212626 1.4913617 1.9444827 0 .099987 31 2004 0 29 0 1.624644 .253375 .7781513 1.230449 .002465 .143688 31 2005 2007 29 1 1.971265 .146475 1 .90309 .004496 .091685 31 2010 0 28 0 . . . . 0 . 31 2012 0 28 0 . . . . 0 . 32 2011 0 24 0 19.825905 .345059 1.0791812 1.0413927 0 2.109665 33 2016 0 23 0 . . . . 0 . 34 2001 0 29 0 1.597229 .124661 1.4913617 .69897 .005225 .091507 34 2003 0 29 1 1.248475 .128721 1.518514 .69897 .003861 .014222 34 2007 0 29 0 2.352989 .162159 1.5682018 .7781513 0 .019449 35 2006 0 29 0 . .08645 . .60206 .001236 .002973 36 2001 0 22 0 2.873395 1.502492 1.361728 1.1139433 0 . 36 2011 0 18 1 6.4555 1.67647 1.518514 .845098 0 .01 36 2013 0 18 0 1.915 1.797204 1.544068 .60206 0 .0001 37 2000 0 20 0 4.925713 .161166 .4771213 .90309 .010096 .094884 37 2004 0 20 0 9.116494 .553086 .7781513 1.2787536 0 .073394 37 2015 2004 16 1 13.910444 1.623544 1.2552725 1.2787536 .0246 .176015 38 2008 0 16 0 . . . . . . 39 2004 0 24 0 12.521506 .371493 .69897 .9542425 .020585 .215058 39 2006 0 24 0 11.968766 .383766 . .9542425 .068368 .679893 39 2013 0 21 1 37.733746 .9756 1.146128 1.146128 .139583 11.572277 40 2015 0 27 0 28.32559 1.0265 1.2787536 1.0413927 .04085 .234797 41 2007 0 28 0 . . . . . . 41 2008 0 28 0 . . . . . . 42 2003 2007 26 0 .479929 .186855 1.462398 .9542425 0 .035833 end
The results are given as follows
Code:
Difference-in-difference with Multiple Time Periods
Number of obs = 259,688
Outcome model : weighted least squares
Treatment model: inverse probability tilting
------------------------------------------------------------------------------
| Coefficient Std. err. z P>|z| [95% conf. interval]
-------------+----------------------------------------------------------------
g2001 |
t_2000_2001 | .1359192 .0621955 2.19 0.029 .0140181 .2578202
t_2000_2002 | -.0143439 .07478 -0.19 0.848 -.16091 .1322223
t_2000_2003 | -.0105746 .0765242 -0.14 0.890 -.1605593 .1394102
t_2000_2004 | -.0514159 .0805613 -0.64 0.523 -.2093131 .1064813
t_2000_2005 | -.0658185 .0808156 -0.81 0.415 -.2242143 .0925772
t_2000_2006 | -.0250564 .0982197 -0.26 0.799 -.2175635 .1674507
t_2000_2007 | -.0843757 .098585 -0.86 0.392 -.2775988 .1088474
t_2000_2008 | -.098825 .077998 -1.27 0.205 -.2516984 .0540483
t_2000_2009 | -.9833446 .2562036 -3.84 0.000 -1.485494 -.4811948
t_2000_2010 | -.5326917 .2389841 -2.23 0.026 -1.001092 -.0642914
t_2000_2011 | -.5221836 .2695765 -1.94 0.053 -1.050544 .0061766
t_2000_2012 | -.3561925 .3888814 -0.92 0.360 -1.118386 .406001
t_2000_2013 | -.4737229 .2655639 -1.78 0.074 -.9942185 .0467727
t_2000_2014 | .2497362 .2746382 0.91 0.363 -.2885447 .7880172
t_2000_2015 | -.4644953 .5426943 -0.86 0.392 -1.528157 .5991661
t_2000_2016 | -.725259 .2754092 -2.63 0.008 -1.265051 -.185467
-------------+----------------------------------------------------------------
g2002 |
t_2000_2001 | .031805 .1008373 0.32 0.752 -.1658325 .2294425
t_2001_2002 | -.0125219 .1029175 -0.12 0.903 -.2142366 .1891928
t_2001_2003 | .0314046 .1078186 0.29 0.771 -.1799161 .2427252
t_2001_2004 | .1040843 .1094818 0.95 0.342 -.1104961 .3186647
t_2001_2005 | .0969999 .1119865 0.87 0.386 -.1224896 .3164894
t_2001_2006 | -.0618612 .1393739 -0.44 0.657 -.335029 .2113066
t_2001_2007 | .0360803 .1099418 0.33 0.743 -.1794016 .2515622
t_2001_2008 | -.012087 .2042771 -0.06 0.953 -.4124627 .3882887
t_2001_2009 | .0701141 .1704975 0.41 0.681 -.2640548 .4042829
t_2001_2010 | .0329867 .2012414 0.16 0.870 -.3614391 .4274125
t_2001_2011 | -.0635331 .1721906 -0.37 0.712 -.4010205 .2739542
t_2001_2012 | -.0880607 .2028776 -0.43 0.664 -.4856934 .3095721
t_2001_2013 | .0885974 .1769585 0.50 0.617 -.2582348 .4354297
t_2001_2014 | .0060436 .2080253 0.03 0.977 -.4016786 .4137657
t_2001_2015 | .150378 .2124906 0.71 0.479 -.2660959 .566852
t_2001_2016 | -.061684 .2031478 -0.30 0.761 -.4598465 .3364784
-------------+----------------------------------------------------------------
g2003 |
t_2000_2001 | .0635357 .055319 1.15 0.251 -.0448875 .1719589
t_2001_2002 | -.0225353 .0453873 -0.50 0.620 -.1114927 .0664221
t_2002_2003 | -.0555034 .0427832 -1.30 0.195 -.1393569 .02835
t_2002_2004 | .0380495 .0380121 1.00 0.317 -.0364528 .1125518
t_2002_2005 | .053506 .0458522 1.17 0.243 -.0363627 .1433747
t_2002_2006 | -.0810894 .0445366 -1.82 0.069 -.1683796 .0062008
t_2002_2007 | -.0556055 .0514164 -1.08 0.279 -.1563798 .0451688
t_2002_2008 | -.0277501 .0631678 -0.44 0.660 -.1515568 .0960566
t_2002_2009 | -.2249484 .0610121 -3.69 0.000 -.3445298 -.1053669
t_2002_2010 | -.0594102 .0679527 -0.87 0.382 -.1925949 .0737746
t_2002_2011 | .1760359 .0764686 2.30 0.021 .0261602 .3259117
t_2002_2012 | .1491032 .080763 1.85 0.065 -.0091893 .3073957
t_2002_2013 | .1239421 .0771465 1.61 0.108 -.0272622 .2751465
t_2002_2014 | .0950071 .0869983 1.09 0.275 -.0755064 .2655207
t_2002_2015 | .2268097 .0771803 2.94 0.003 .0755391 .3780802
t_2002_2016 | .1719427 .0865987 1.99 0.047 .0022124 .341673
-------------+----------------------------------------------------------------
g2004 |
t_2000_2001 | .1271993 .0782127 1.63 0.104 -.0260948 .2804934
t_2001_2002 | .0221214 .0511829 0.43 0.666 -.0781953 .1224381
t_2002_2003 | .0050338 .0501657 0.10 0.920 -.0932891 .1033568
t_2003_2004 | .0520257 .0472925 1.10 0.271 -.0406659 .1447172
t_2003_2005 | -.0473713 .0566435 -0.84 0.403 -.1583906 .063648
t_2003_2006 | -.0105437 .0650697 -0.16 0.871 -.1380779 .1169906
t_2003_2007 | .0510087 .0719207 0.71 0.478 -.0899534 .1919707
t_2003_2008 | .0320615 .0725415 0.44 0.659 -.1101172 .1742403
t_2003_2009 | -.0072776 .0637816 -0.11 0.909 -.1322873 .117732
t_2003_2010 | -.1175541 .0749426 -1.57 0.117 -.2644389 .0293307
t_2003_2011 | -.0665618 .0696885 -0.96 0.340 -.2031488 .0700252
t_2003_2012 | -.043953 .0823595 -0.53 0.594 -.2053746 .1174685
t_2003_2013 | -.1752867 .0880281 -1.99 0.046 -.3478186 -.0027548
t_2003_2014 | -.1387435 .0908543 -1.53 0.127 -.3168147 .0393277
t_2003_2015 | -.0475867 .0785583 -0.61 0.545 -.2015581 .1063847
t_2003_2016 | -.1212173 .0806625 -1.50 0.133 -.2793129 .0368783
-------------+----------------------------------------------------------------
g2005 |
t_2000_2001 | .2680297 .0449572 5.96 0.000 .1799152 .3561441
t_2001_2002 | .1012079 .0344085 2.94 0.003 .0337685 .1686473
t_2002_2003 | .0935386 .0336224 2.78 0.005 .0276399 .1594373
t_2003_2004 | -.0570501 .0316667 -1.80 0.072 -.1191158 .0050155
t_2004_2005 | .0040703 .0310998 0.13 0.896 -.0568842 .0650248
t_2004_2006 | .0863945 .0344813 2.51 0.012 .0188123 .1539767
t_2004_2007 | -.0539247 .0363731 -1.48 0.138 -.1252147 .0173652
t_2004_2008 | -.0351034 .0413831 -0.85 0.396 -.1162127 .046006
t_2004_2009 | -.1233207 .0652567 -1.89 0.059 -.2512215 .00458
t_2004_2010 | -.2118638 .0684857 -3.09 0.002 -.3460933 -.0776343
t_2004_2011 | -.0441961 .066355 -0.67 0.505 -.1742495 .0858574
t_2004_2012 | -.0911695 .0671303 -1.36 0.174 -.2227424 .0404034
t_2004_2013 | -.1028625 .0558414 -1.84 0.065 -.2123096 .0065847
t_2004_2014 | .0463188 .0598184 0.77 0.439 -.0709231 .1635606
t_2004_2015 | -.1071424 .0654272 -1.64 0.102 -.2353774 .0210927
t_2004_2016 | -.1068519 .0674937 -1.58 0.113 -.239137 .0254333
-------------+----------------------------------------------------------------
g2006 |
t_2000_2001 | .1232365 .0598827 2.06 0.040 .0058685 .2406045
t_2001_2002 | .0400035 .0408842 0.98 0.328 -.0401281 .1201351
t_2002_2003 | .0889734 .0397942 2.24 0.025 .0109781 .1669687
t_2003_2004 | .0341207 .0328661 1.04 0.299 -.0302956 .0985371
t_2004_2005 | .0009825 .0359732 0.03 0.978 -.0695236 .0714886
t_2005_2006 | -.0152202 .0400846 -0.38 0.704 -.0937847 .0633442
t_2005_2007 | -.0408244 .0394765 -1.03 0.301 -.1181968 .036548
t_2005_2008 | -.0642229 .0397772 -1.61 0.106 -.1421847 .013739
t_2005_2009 | -.0493849 .0453972 -1.09 0.277 -.1383618 .039592
t_2005_2010 | -.0319465 .0477733 -0.67 0.504 -.1255804 .0616874
t_2005_2011 | .0085074 .0498981 0.17 0.865 -.0892911 .106306
t_2005_2012 | .0035198 .0564838 0.06 0.950 -.1071865 .1142261
t_2005_2013 | -.0255086 .0586193 -0.44 0.663 -.1404003 .0893832
t_2005_2014 | -.0189691 .0546017 -0.35 0.728 -.1259864 .0880483
t_2005_2015 | -.0805522 .0579372 -1.39 0.164 -.1941071 .0330027
t_2005_2016 | -.1869213 .0612938 -3.05 0.002 -.307055 -.0667877
-------------+----------------------------------------------------------------
g2007 |
t_2000_2001 | .1159431 .0334805 3.46 0.001 .0503224 .1815637
t_2001_2002 | .0015658 .0235831 0.07 0.947 -.0446563 .0477879
t_2002_2003 | -.0120483 .0220182 -0.55 0.584 -.0552031 .0311065
t_2003_2004 | -.0676286 .0200516 -3.37 0.001 -.1069289 -.0283283
t_2004_2005 | .0552464 .0209224 2.64 0.008 .0142392 .0962536
t_2005_2006 | -.0020063 .0253267 -0.08 0.937 -.0516457 .0476331
t_2006_2007 | -.0258757 .0231581 -1.12 0.264 -.0712647 .0195132
t_2006_2008 | -.048854 .0221473 -2.21 0.027 -.092262 -.0054461
t_2006_2009 | -.0843969 .0279537 -3.02 0.003 -.139185 -.0296087
t_2006_2010 | -.0273271 .0284485 -0.96 0.337 -.0830852 .0284309
t_2006_2011 | -.0811503 .0302581 -2.68 0.007 -.1404551 -.0218454
t_2006_2012 | -.1127431 .0312965 -3.60 0.000 -.1740832 -.051403
t_2006_2013 | -.166824 .0286388 -5.83 0.000 -.222955 -.110693
t_2006_2014 | -.1396882 .0285856 -4.89 0.000 -.195715 -.0836615
t_2006_2015 | -.1323348 .0287092 -4.61 0.000 -.1886037 -.0760658
t_2006_2016 | -.1234311 .0294373 -4.19 0.000 -.1811272 -.065735
-------------+----------------------------------------------------------------
g2008 |
t_2000_2001 | .0722769 .060174 1.20 0.230 -.045662 .1902158
t_2001_2002 | .0038559 .0384896 0.10 0.920 -.0715823 .079294
t_2002_2003 | -.0118115 .0366117 -0.32 0.747 -.083569 .0599461
t_2003_2004 | -.046244 .0330262 -1.40 0.161 -.1109742 .0184863
t_2004_2005 | -.0543827 .035234 -1.54 0.123 -.1234401 .0146748
t_2005_2006 | .0407007 .0402204 1.01 0.312 -.0381298 .1195312
t_2006_2007 | -.0711688 .0336985 -2.11 0.035 -.1372166 -.0051209
t_2007_2008 | -.0309405 .0311763 -0.99 0.321 -.0920449 .0301639
t_2007_2009 | -.0905782 .0419773 -2.16 0.031 -.1728521 -.0083043
t_2007_2010 | -.0960392 .0422405 -2.27 0.023 -.178829 -.0132494
t_2007_2011 | -.0505039 .0477632 -1.06 0.290 -.1441179 .0431102
t_2007_2012 | .0753368 .0462555 1.63 0.103 -.0153224 .1659959
t_2007_2013 | .0436011 .0429333 1.02 0.310 -.0405466 .1277488
t_2007_2014 | .0316045 .0432932 0.73 0.465 -.0532486 .1164577
t_2007_2015 | -.083984 .0417578 -2.01 0.044 -.1658278 -.0021402
t_2007_2016 | -.067727 .047513 -1.43 0.154 -.1608509 .0253968
-------------+----------------------------------------------------------------
g2009 |
t_2000_2001 | -.127822 .0596671 -2.14 0.032 -.2447674 -.0108765
t_2001_2002 | -.0285082 .0857839 -0.33 0.740 -.1966416 .1396252
t_2002_2003 | -.0638373 .0361383 -1.77 0.077 -.1346671 .0069924
t_2003_2004 | .0823688 .0460726 1.79 0.074 -.0079319 .1726695
t_2004_2005 | .0422674 .0482661 0.88 0.381 -.0523324 .1368673
t_2005_2006 | .1152176 .0538368 2.14 0.032 .0096994 .2207357
t_2006_2007 | .0060913 .0323101 0.19 0.850 -.0572353 .069418
t_2007_2008 | -.0046828 .0331351 -0.14 0.888 -.0696263 .0602608
t_2008_2009 | -.2065412 .0112974 -18.28 0.000 -.2286837 -.1843987
t_2008_2010 | .9735072 .0109739 88.71 0.000 .9519987 .9950158
t_2008_2011 | .7071898 .012179 58.07 0.000 .6833195 .7310601
t_2008_2012 | .2882963 .3745125 0.77 0.441 -.4457348 1.022327
t_2008_2013 | .8959242 .0133906 66.91 0.000 .8696791 .9221694
t_2008_2014 | -.5359192 .3513669 -1.53 0.127 -1.224586 .1527473
t_2008_2015 | -.443043 .362458 -1.22 0.222 -1.153448 .2673616
t_2008_2016 | .1456931 .0129057 11.29 0.000 .1203984 .1709879
------------------------------------------------------------------------------
Control: Never Treated
See Callaway and Sant'Anna (2021) for details
[/CODE]
Code:
estat all
This command provides the post estimation results
Code:
estat all
Pretrend Test. H0 All Pre-treatment are equal to 0
chi2(36) = 138.9884
p-value = 0.0000
Average Treatment Effect on Treated
------------------------------------------------------------------------------
| Coefficient Std. err. z P>|z| [95% conf. interval]
-------------+----------------------------------------------------------------
ATT | -.0442555 .0095415 -4.64 0.000 -.0629565 -.0255546
------------------------------------------------------------------------------
ATT by group
------------------------------------------------------------------------------
| Coefficient Std. err. z P>|z| [95% conf. interval]
-------------+----------------------------------------------------------------
GAverage | 0 (omitted)
G2001 | .0015428 .0370844 0.04 0.967 -.0711414 .0742269
G2002 | .0337824 .0597963 0.56 0.572 -.0834162 .1509809
G2003 | -.0124421 .024485 -0.51 0.611 -.0604319 .0355476
G2004 | -.0016421 .0365629 -0.04 0.964 -.0733041 .0700199
G2005 | -.009556 .0232204 -0.41 0.681 -.0550671 .0359551
G2006 | -.0463602 .0275407 -1.68 0.092 -.1003389 .0076185
G2007 | -.0796073 .0159631 -4.99 0.000 -.1108945 -.0483202
G2008 | -.0292721 .0242011 -1.21 0.226 -.0767054 .0181612
G2009 | 0 (omitted)
------------------------------------------------------------------------------
ATT by Calendar Period
------------------------------------------------------------------------------
| Coefficient Std. err. z P>|z| [95% conf. interval]
-------------+----------------------------------------------------------------
CAverage | -.0347443 .0105736 -3.29 0.001 -.0554681 -.0140206
T2001 | .1359192 .0621955 2.19 0.029 .0140181 .2578202
T2002 | -.0139968 .063638 -0.22 0.826 -.1387251 .1107314
T2003 | -.0435932 .0363432 -1.20 0.230 -.1148247 .0276382
T2004 | .0384144 .0275295 1.40 0.163 -.0155424 .0923711
T2005 | .0063183 .0235598 0.27 0.789 -.039858 .0524946
T2006 | .0295195 .0236949 1.25 0.213 -.0169216 .0759606
T2007 | -.0332407 .0169693 -1.96 0.050 -.0665 .0000186
T2008 | -.0416617 .0152235 -2.74 0.006 -.0714993 -.0118241
T2009 | -.1033573 .0202208 -5.11 0.000 -.1429894 -.0637253
T2010 | -.0546697 .0209572 -2.61 0.009 -.0957449 -.0135944
T2011 | -.0560698 .0221228 -2.53 0.011 -.0994297 -.0127099
T2012 | -.0598251 .0240479 -2.49 0.013 -.106958 -.0126921
T2013 | -.0969631 .0221744 -4.37 0.000 -.1404241 -.0535022
T2014 | -.0685095 .0220662 -3.10 0.002 -.1117584 -.0252605
T2015 | -.0969491 .0215334 -4.50 0.000 -.1391537 -.0547445
T2016 | -.0972448 .0222988 -4.36 0.000 -.1409496 -.05354
------------------------------------------------------------------------------
ATT by Periods Before and After treatment
Event Study:Dynamic effects
------------------------------------------------------------------------------
| Coefficient Std. err. z P>|z| [95% conf. interval]
-------------+----------------------------------------------------------------
Pre_avg | -.0036284 . . . . .
Post_avg | -.0324081 . . . . .
Tm8 | -.127822 .0596671 -2.14 0.032 -.2447674 -.0108765
Tm7 | -.0172815 .0765523 -0.23 0.821 -.1673212 .1327582
Tm6 | -.0192933 .0258435 -0.75 0.455 -.0699456 .031359
Tm5 | .0498549 .0270501 1.84 0.065 -.0031623 .102872
Tm4 | .0301359 .023802 1.27 0.205 -.0165151 .0767869
Tm3 | .0337756 .0223595 1.51 0.131 -.0100482 .0775995
Tm2 | .0394766 .014706 2.68 0.007 .0106533 .0682998
Tm1 | -.0178738 .0158158 -1.13 0.258 -.0488722 .0131247
Tp0 | -.008854 .0134861 -0.66 0.511 -.0352862 .0175783
Tp1 | -.0130994 .0144893 -0.90 0.366 -.0414979 .0152991
Tp2 | -.0514482 .0164238 -3.13 0.002 -.0836381 -.0192582
Tp3 | -.0357619 .017385 -2.06 0.040 -.069836 -.0016879
Tp4 | -.0488227 .0203288 -2.40 0.016 -.0886664 -.0089789
Tp5 | -.0619688 .021043 -2.94 0.003 -.1032124 -.0207252
Tp6 | -.1118036 .0206946 -5.40 0.000 -.1523643 -.071243
Tp7 | -.1059614 .0196923 -5.38 0.000 -.1445575 -.0673653
Tp8 | -.0970031 .0215784 -4.50 0.000 -.1392959 -.0547103
Tp9 | -.0876707 .0246519 -3.56 0.000 -.1359875 -.0393539
Tp10 | -.0880489 .0432392 -2.04 0.042 -.1727961 -.0033017
Tp11 | -.0323774 .0629766 -0.51 0.607 -.1558092 .0910544
Tp12 | .0523483 .0803156 0.65 0.515 -.1050673 .209764
Tp13 | .1719427 .0865987 1.99 0.047 .0022124 .341673
Tp14 | 0 (omitted)
Tp15 | 0 (omitted)
1) I understand that here parallel trend is not satisfied . Can adding more co-variates help in ensuring the parallel trend? Once I try with more covariates (including dummy variables), much of the treatment effects in the long table I gave above gets omitted. What would be the reason and is thee any way to rectify this ?
2) My second question is that if firms are anticipating a policy change make changes in the product portfolio before the policy gets implemented, can we take care of such an anticipatory effect in the did equation ?
Thank you so much in advance
