Dear Stata members

I would like to ask the community to share their thoughts on using levels instead of changes relating to variables while invoking fixed effects. Thus is it correct to run regression
1. (Debtt- Debtt-1) /Total assets as a dependent variable with firm fixed effects and year dummies
OR
2. Debt/Total assets as a dependent variable with firm fixed effects and year dummies

Let me give a sample dataset and the results

Code:
* Example generated by -dataex-. For more info, type help dataex
clear
input long code int year float(debt totass nsales cashban)
   11 2011    1206  2191.1  2544.6     112
   11 2012  1586.8  2784.9    3014    91.4
   11 2013  1648.4  3057.6  3121.9    63.9
   11 2014  1767.2    3425  3278.5      92
   11 2015  1665.4  3498.9  3565.2     184
   11 2016  1634.2  3532.9  3573.3    93.9
   11 2017  1522.9  3900.3  3907.1     122
   11 2018  1345.3    4068  4258.2   105.6
   11 2019  1244.6  4383.7  4793.7     113
  289 2011     897  1658.2  2084.9    87.9
  289 2012   970.3  1746.5  2552.1    78.5
  289 2013   781.3    1522  1767.9    47.9
  289 2014   655.5  1349.4  1613.9    41.1
  363 2011  5522.6 11598.8  2268.4  1251.2
  363 2012    5084 10745.7  2518.6  1160.4
  363 2013  6046.2   11366  1672.5   412.7
  363 2014  5591.8 11196.6  1065.4   583.8
  363 2015  5108.9  9910.3  1088.5     629
  363 2016  5289.9 10009.8  1169.9   239.3
  363 2017  5551.8  9490.9   995.3   262.8
  363 2018  4247.8  9618.1    3711   202.9
  363 2019  6453.3  9361.4  1254.6   172.9
  414 2016   219.4     483  1089.3    98.1
  414 2017     2.5   389.4  1423.1    60.1
  414 2018     1.8   322.7   886.4    60.6
  415 2018       .  1981.9   619.6    73.7
  415 2019       .  1874.7   604.9   358.9
  771 2013   352.6     758   572.5    39.7
  771 2014   515.2   990.1     788    52.2
  771 2015   567.1  1228.3  1077.3   110.8
  771 2016   984.8  1799.1  1324.9   106.3
  771 2017  1176.8  2155.4  1439.3   105.1
  771 2018  1175.2  2373.5  1403.8   101.7
  771 2019  1218.1  2622.1  1762.4   194.1
  783 2011   341.8  1723.5  1283.4   208.4
  783 2012   380.1  1816.7  1553.5   200.9
  783 2013   436.7  2208.3  1782.4   133.6
  783 2014   283.9  2182.6  2070.7   126.2
  783 2015   189.5  2183.8  2025.3   108.8
  783 2016    72.6    2179  2089.5    93.1
  783 2017    55.2  2148.1  2007.5   138.3
  783 2018    31.3  2149.7  2083.1   317.9
  783 2019       2  2042.7  2433.6     184
 1120 2011   211.5 12945.2 11594.1  1530.6
 1120 2012     480 14937.2 14159.4  1501.1
 1120 2013  1609.6 18524.6 17505.2  2807.8
 1120 2014  1206.2 22357.9 20788.3  2199.2
 1120 2015   986.2 25511.6 21819.1  1897.6
 1120 2016  1837.8   27984 20970.3  1241.3
 1120 2017  1402.1   32081   22398  2477.9
 1120 2018  1234.3 35691.3 24426.1    2650
 1120 2019  1282.7 40503.9 30719.8  2163.2
 2248 2017   413.9  2791.9  2486.1    15.8
 2248 2018   470.2  3008.9  2720.9    20.3
 2717 2011 10862.9 27241.1 13842.9  3385.1
 2717 2012 14223.7 26358.5 18895.6  3988.4
 2717 2013 16455.5 31555.2 19001.2  3741.9
 2717 2014 14241.2 27709.6 22572.6  3499.6
 2717 2015 15050.4 31702.5 24580.6  4452.9
 2717 2016 12312.8 39717.1 28932.3  3419.1
 2717 2017 11369.2 43337.1 30106.6  2926.1
 2717 2018 34008.7  153908   46070  5862.7
 2717 2019 28086.1  146343 61632.7  1828.5
 2842 2011   164.6   659.7  1116.1    64.9
 2842 2012     335   871.9  1454.5    92.4
 2842 2013   391.1  1079.5  1749.7    93.5
 2842 2014   443.1  1172.1  1666.1    83.3
 2842 2015   430.2    1178  1637.2     100
 2842 2016   172.7   901.6   625.8   131.2
 2842 2017     7.5   617.9   813.4    71.1
 2842 2018    79.5   693.2   825.4    17.5
 2842 2019   147.1   864.7   890.7   104.5
 3335 2011   558.7  1399.2    1459    26.5
 3335 2012   387.5  1962.2  2481.1    78.4
 3335 2013     355    2284  2677.8    90.8
 3335 2014    54.6  2388.1    2907   155.9
 3335 2015      68  2382.3  2542.6   150.7
 3335 2016    97.5  2505.9  2689.4     112
 3335 2017   153.2  2772.8  3098.2   126.5
 3335 2018   360.7  3321.9  3268.2    90.4
 3335 2019   814.2  3918.8  3377.2   117.3
 3990 2011  2674.8  5235.1  5010.6    52.7
 3990 2015    4479 10051.1 10942.7    35.8
 3990 2016  4834.1 11028.9 11348.9    48.3
 3990 2017  4831.4 11910.4 11951.7    41.8
 3990 2018  5498.9 13901.6 12436.3    42.7
 3990 2019    5099 14559.1 15609.4    55.6
 3998 2011  5285.3   13991 14523.6   128.7
 3998 2012  6279.5 16611.5 16722.8   105.6
 3998 2013  8505.1 21759.9 20937.7   124.2
 3998 2014 10467.7 26701.3 26324.7   148.6
 3998 2015 12022.5 29385.6 29079.4   337.1
 3998 2016 12917.6 29668.1 30067.2   289.9
 3998 2017 15644.5 35009.8 31612.9     285
 3998 2018 20831.7 43914.5 38053.5     321
 3998 2019 24012.3 58579.4 41676.3  5839.8
 4024 2018  3793.4  9195.7  8260.4   230.9
 4024 2019  4342.2    9639  7508.9   175.4
 4030 2016    94.3   525.5  1101.6      40
 4030 2017     145     834  1531.7    66.4
 4030 2018    39.3  1030.9  1734.4   159.7
 4030 2019    81.5  1072.7  2060.1    89.4
 4253 2011  133738  161118 33452.6  5950.6
 4253 2012  138563  174367   31612  1343.9
 4253 2013  139615  183003 36719.5    1491
 4253 2014  148554  202496 39342.6  1479.6
 4253 2015  143481  212612   40407  1177.2
 4253 2016  147260  206305 33339.2  1342.1
 4253 2017  148265  187277 17543.6   946.1
 4253 2018  157117  169377 14650.1   842.4
 4253 2019  174717  136854  8475.1   728.1
 4671 2016  9609.1   26413 16036.4   144.9
 4671 2017  8012.2 24671.6 16264.5   149.4
 4671 2018  5935.1 23826.2 17381.7     245
 4671 2019  3374.4 23116.3 20411.2   190.1
 4709 2012 22836.5 34277.7   27394   230.3
 4709 2013 22398.1 34175.5 33370.4   335.7
 4709 2014 18622.7 33484.3 38657.1   250.1
 4709 2015 25801.4 47409.1 37859.7   170.1
 4709 2016 35026.6 69299.2 36712.3   819.4
 4709 2017 28494.1 64290.2   46216  1326.4
 4709 2018 27978.1 62933.2 45653.4  1665.5
 4709 2019 24357.5 61972.9 52437.2   257.2
 5003 2011   324.8  2974.9  3945.8   289.3
 5003 2012  1008.1  3460.2  4823.4   117.1
 5003 2013  1083.7  3606.5  3951.8     268
 5003 2014    1557  3799.9  4194.3   199.5
 5003 2015  1984.7  4703.8  4840.3   472.5
 5003 2016  2127.8  3678.1  5092.3   421.8
 5003 2017  2565.1  4151.5  4922.5   562.1
 5003 2018  1824.3  3037.2  4833.9   220.3
 5003 2019    1778  3909.9  5450.5   214.7
 5284 2011     3.1   170.2    17.6     6.4
 5284 2012     1.7   173.2    25.3     9.3
 5284 2013     2.1   173.7    38.4     9.5
 5284 2014      .5   182.2    47.5    12.6
 5284 2015       .   193.9    59.4     9.6
 5284 2016      .5   204.3    80.9     8.5
 5284 2017       .   225.2    84.7     7.5
 5284 2018       .   240.6    87.4     7.4
 5284 2019     3.5   263.6    80.8    11.2
 5574 2011   211.6   607.9   551.6    12.7
 5574 2012   234.5   619.7   616.5      20
 5574 2013   310.8   791.8   784.8    21.9
 5574 2014   391.7   981.3  1040.6    24.1
 5574 2015   729.5  1480.9  1270.9    66.9
 5574 2016   672.5  2003.6    1731   284.5
 5574 2017   800.8  2409.2  1809.6   222.3
 5574 2018   916.2  2680.4  1963.9   174.4
 5574 2019   968.8  2994.9  2515.6   139.9
 5747 2011  333750  641331  263300 28502.5
 5747 2012  692325 1100000  391570 69707.3
 5747 2013  693318 1100000  463023 72388.5
 5747 2014  719799 1200000  548869 38739.4
 5747 2015  835706 1300000  644144   37189
 5747 2016  191694  417704  339139   15395
 5747 2017  208457  477452  365142 17150.9
 5747 2018  176367  566000  358946 18842.5
 5747 2019  116317  431150  402893 17092.8
 5757 2011  245027  352616 20864.1  9643.2
 5757 2012  386003  513941   39424 36669.3
 5757 2013  417955  547011 66616.1   18724
 5757 2014  441502  622419  153261  9413.3
 5757 2015  448396  640669  186828  8916.4
 5757 2016  528778  831851  251477  8938.3
 5757 2017  524844  790838  225611  6659.3
 5757 2018  530426  752180  203099  9223.1
 5757 2019  469799  745419  238978 10201.6
 5838 2017    14.8    85.5     4.9      .7
 5838 2018      11    90.5      11      .3
 5838 2019    31.7   106.7     5.2      .1
 6584 2014       .  1205.5  1406.3   252.1
 6584 2015       .  1297.2  1392.8   322.8
 6584 2016     8.6  1339.4  1449.6   297.8
 6584 2017    22.4  1316.2  1465.5   249.6
 6584 2018    21.8  1314.1  1520.4   266.6
 6584 2019    30.1  1390.1  1856.4   259.9
 6585 2016    23.2    62.5    56.5     5.3
 6585 2017    25.7   102.5      67     5.1
 6585 2018       5    62.4    65.8     6.1
 6585 2019     5.9    87.6    72.8       6
 6819 2011   651.6  1542.5  1165.9   148.8
 6819 2013  1843.7  3978.3  2200.5      38
 6819 2014  1685.4    4063  2385.1    27.6
 6819 2015  1150.3  4171.8  2219.5    43.6
 6819 2016  1013.5  4520.2  2922.3   264.5
 6819 2017   540.5  5830.4  3291.8    80.1
 6819 2018   667.7  7337.6  3872.1   614.4
 6819 2019   350.3  8126.5  4150.4   234.1
 6923 2013    96.8  2672.8  3644.3    53.6
 6923 2014   185.8  3149.8  3710.7   222.9
 6923 2015     4.9  3183.9  3884.1   204.6
 6923 2016       2  3738.2    4081   151.7
 6923 2017   356.4  4190.4  4425.2   236.1
 6923 2018   813.2  4674.4  4660.1   209.5
 6923 2019   649.9  4717.3  5147.1   334.5
 7068 2011  1243.5  5513.5 18085.8   867.9
 7068 2012 21094.2 29597.2 44615.7 19120.2
 7068 2013  3318.7 10096.2 39777.8  2045.5
 7068 2014  2409.7  8915.7 50282.5   725.6
 7068 2015  2180.9  9413.9 39137.8    1054
 7068 2016  1883.6  9043.7   22110   966.9
 7068 2017  2864.6 20362.5 39256.9   622.8
 7068 2018  3040.4   22147 47885.5  1619.9
 7068 2019  2387.7   24476 56133.4  4129.2
 7077 2011   105.7  1017.4  3142.6    25.3
 7077 2012    14.9   847.4  2807.7    49.6
 7077 2013    80.3   954.6  2747.5    26.4
 7077 2014    90.7  1008.8  2748.5    28.5
 7077 2015   238.4    1210  2318.2    41.5
 7077 2016   403.3  1271.6  3552.8    34.7
 7077 2017   453.9  2450.4  3558.5    34.5
 7077 2018   636.1  2610.3  3329.3    43.7
 7633 2013   702.4  7079.9 40132.2   735.6
 7633 2014  1236.7  7965.5 17340.6   886.8
 7633 2015  1821.7 10231.9   31982  1742.9
 7633 2016    2367 10310.3   39315   812.2
 7633 2017  5926.9   11085 49355.1   774.3
 7633 2018  3995.1    8068 52971.2   538.7
 7633 2019  5762.8  9847.4 42622.9   812.3
 8183 2011       .  2814.7  7145.9   447.6
 8183 2012       .  2876.1  6996.3     410
 8183 2013       .  3340.8  7821.5   109.7
 8183 2014     150  3852.8  7583.5    63.4
 8183 2015   258.6  4344.8  7520.6    96.5
 8183 2016   956.5  5174.6    7759    66.6
 8183 2017   176.2    4259  7978.6    43.6
 8183 2018       .  4500.5  8417.7   308.1
 8183 2019       .  4845.3    8640    48.7
 8312 2011    2043 11582.5   17543  1504.8
 8312 2012  2483.1 11745.8   14469   988.5
 8312 2013    2745 10794.9 14357.2   926.4
 8312 2014  2388.5 10539.6    9605   632.2
 8312 2015  1734.5 10455.5 10598.8   903.1
 8312 2016  1427.3 11599.5 12494.5   967.2
 8312 2017   901.6 12402.2 14261.6  1385.8
 8312 2018     298 12635.4 16461.4  1369.9
 8312 2019   611.1 14981.8 17542.5  2194.3
 8523 2014    15.7   651.8  1399.4    23.8
 8523 2015    13.6   532.5  1643.4    16.4
 8523 2016      .3     584   953.9    25.3
 8523 2017     7.6   628.7   986.3     4.4
 8523 2018    13.4   752.9  1097.8    18.8
 8523 2019     7.9  1101.5  2019.1    37.1
 8628 2017   126.7   506.4   288.2   130.4
 8628 2018   151.7   994.9   371.2    18.9
 8628 2019   110.3   971.2   483.5      27
 8893 2011  1906.4  5301.2  4980.9   147.7
 8893 2012  1996.4  6505.3  6759.1   125.8
 8893 2013  1248.4    7189  9306.1   529.8
 8893 2014  1304.9  9494.7   12074   683.1
 8893 2015   723.8 11480.5 14732.5  1411.6
 8893 2016   929.4 14995.5 17335.9   582.3
 8893 2017    68.1 18646.2 19827.2     713
 8893 2018    41.2 24753.9   21248   969.8
 8893 2019   542.5 29736.7 20547.6  1030.5
 9395 2011   436.4  3785.6 12075.9   336.2
 9395 2012  1708.5  5481.3 18549.4   546.5
 9395 2013    2452  6863.9   28296   719.5
 9395 2014  4005.9  8752.2 40847.8  1170.1
 9395 2015    3355  9207.7   25245    1146
 9395 2016  2554.3  6745.3 19143.4  1204.3
 9395 2017  3367.7 10558.5 15403.9  1233.9
 9395 2018    3974 10083.6  7128.1  1054.1
 9395 2019    2632  8689.3 11717.8   401.8
 9505 2016   106.7   701.3   862.2    88.4
 9505 2017    58.7   960.8  1105.6     161
 9505 2018   261.4  1330.6  1581.4   152.8
 9505 2019   242.9  1485.3   916.8   157.1
 9793 2011  1051.3  4935.8  1309.6     106
 9793 2012  1109.9  5309.8  2727.7   133.7
 9793 2013     890  5479.2  2517.9     141
 9793 2014  1314.3  5808.6  2380.5   153.3
 9793 2015  1378.4  6491.8  3547.9   201.6
 9793 2016  1037.7  6734.6  4456.3   250.3
 9793 2017  1499.4  7658.8  4831.7   101.3
 9793 2018  2701.3  9512.3  6131.6   297.5
 9793 2019  3105.6 10152.3    5284   234.3
10714 2011   148.2   457.1   204.8    14.6
10714 2012   165.5     448   186.9    15.1
10714 2013   120.9   379.4   214.3    12.7
10714 2014    75.4   339.8   261.2    15.3
10714 2015    66.2   340.2   263.2    19.9
10714 2016    92.8   332.3   266.7    23.9
10714 2017    94.5   531.2   256.6    23.5
10714 2018    78.4   668.8   462.5      26
10714 2019    73.6   629.5   647.3    61.7
10735 2018     246   435.9     986     2.2
10735 2019     293   615.4  1164.6     3.4
10867 2018    27.5   292.9     6.8     1.3
10867 2019    27.5   246.1       .      .5
10884 2015 13059.2 53349.1 36822.7 12423.5
10884 2016    6575 55523.7 48859.3 10230.9
10884 2017  6594.6 66935.5 56496.2  7985.6
10884 2018  9975.6 80082.1 63553.5  6597.8
10884 2019  9440.7 86161.3  105061  6981.9
10903 2011  1200.8  2754.6  2351.6    14.7
10903 2012  1235.1  3022.7  2876.9   112.6
10903 2013  1460.1    3709    3644   155.2
10903 2014  1506.5  4377.5  4454.6     240
end

*SETTING PANEL
xtset code year
*GENERATING VARIABLES
gen deb_ta=debt/totass
gen del_deb_ta=d.debt/totass
gen nsal_ta=nsales/totass
gen cash_ta=cashban/totass

 *RUNNING REGRESSION WITH deb_ta as Dep var
 xtreg deb_ta nsal_ta cash_ta i.year, fe vce(robust)

Fixed-effects (within) regression               Number of obs     =        287
Group variable: code                            Number of groups  =         44

R-squared:                                      Obs per group:
     Within  = 0.1126                                         min =          1
     Between = 0.0080                                         avg =        6.5
     Overall = 0.0049                                         max =          9

                                                F(10,43)          =       1.62
corr(u_i, Xb) = -0.1167                         Prob > F          =     0.1342

                                  (Std. err. adjusted for 44 clusters in code)
------------------------------------------------------------------------------
             |               Robust
      deb_ta | Coefficient  std. err.      t    P>|t|     [95% conf. interval]
-------------+----------------------------------------------------------------
     nsal_ta |  -.0079448   .0258297    -0.31   0.760    -.0600354    .0441458
     cash_ta |   .4298472   .2545228     1.69   0.098    -.0834469    .9431413
             |
        year |
       2012  |   .0326785   .0187599     1.74   0.089    -.0051544    .0705114
       2013  |   .0134876   .0261732     0.52   0.609    -.0392957     .066271
       2014  |   -.003149   .0319634    -0.10   0.922    -.0676093    .0613113
       2015  |  -.0206513    .032175    -0.64   0.524    -.0855383    .0442358
       2016  |  -.0172078   .0358528    -0.48   0.634    -.0895118    .0550962
       2017  |  -.0488981   .0409587    -1.19   0.239    -.1314992    .0337031
       2018  |  -.0535187   .0435004    -1.23   0.225    -.1412456    .0342081
       2019  |  -.0506827   .0443039    -1.14   0.259    -.1400301    .0386647
             |
       _cons |   .3030418   .0539048     5.62   0.000     .1943324    .4117512
-------------+----------------------------------------------------------------
     sigma_u |  .19621982
     sigma_e |  .10471008
         rho |  .77835062   (fraction of variance due to u_i)
------------------------------------------------------------------------------



xtreg del_deb_ta nsal_ta cash_ta i.year, fe vce(robust)

Fixed-effects (within) regression               Number of obs     =        239
Group variable: code                            Number of groups  =         43

R-squared:                                      Obs per group:
     Within  = 0.1039                                         min =          1
     Between = 0.0271                                         avg =        5.6
     Overall = 0.0490                                         max =          8

                                                F(9,42)           =       5.24
corr(u_i, Xb) = -0.5162                         Prob > F          =     0.0001

                                  (Std. err. adjusted for 43 clusters in code)
------------------------------------------------------------------------------
             |               Robust
  del_deb_ta | Coefficient  std. err.      t    P>|t|     [95% conf. interval]
-------------+----------------------------------------------------------------
     nsal_ta |  -.0813427    .047161    -1.72   0.092    -.1765174     .013832
     cash_ta |    .327098   .2078102     1.57   0.123    -.0922799    .7464759
             |
        year |
       2013  |  -.1362373    .084005    -1.62   0.112    -.3057662    .0332916
       2014  |  -.0803605   .0236895    -3.39   0.002    -.1281678   -.0325532
       2015  |  -.0893466   .0299759    -2.98   0.005    -.1498403   -.0288529
       2016  |  -.1536604   .0773283    -1.99   0.053    -.3097153    .0023945
       2017  |  -.1061033   .0367209    -2.89   0.006    -.1802092   -.0319975
       2018  |  -.1031997   .0368414    -2.80   0.008    -.1775486   -.0288508
       2019  |  -.0932153   .0397741    -2.34   0.024    -.1734826   -.0129479
             |
       _cons |   .1700746   .0688796     2.47   0.018     .0310699    .3090793
-------------+----------------------------------------------------------------
     sigma_u |   .0868477
     sigma_e |  .18768043
         rho |  .17636537   (fraction of variance due to u_i)
------------------------------------------------------------------------------

Kindly note that when I use Levels, even the model fit is poor (Low F-Stats), but when I use change in debt over assets, we have a better Model fit and the variable of interest (nsal_t) seems to significant preditor.
Other than from the perspective of interpretation, I would like ask,
IF WE HAVE FIXED EFFECTS (BOTH ENTITY AND YEAR), SHOULD WE USE LEVEL OR CHANGE IN LEVEL AS THE DEP VARIABLE?

REFERENCES

"First, including fixed effects can exacerbate measurement problems (Griliches and Mairesse, 1995). Second, if the dependent variable is a first differenced variable, such as investment or the change in corporate cash balances, and if the fixed effect is related to the level of the dependent variable, then the fixed effect has already been differenced out of the regression, and using a fixedeffects specification reduces efficiency. In practice, for example, fixed effects rarely tend to make important qualitative differences on the coefficients in investment regressions (Erickson and Whited, 2012), because investment is (roughly) the first difference of the capital stock. However, fixed effects do make important differences in the estimated coefficients in leverage 77 regressions (Lemmon, Roberts, and Zender, 2008), because leverage is a level and not a change" - Endogeneity in Empirical Corporate Finance (Michael R. Roberts and Toni M. Whited)

"Note that in our experimental design, a fixed-effects specification is not appropriate. By construction, all of the sample firms exhibit a large shift in leverage. Labeling such a shift as a “fixed effect” would mask much of the information about leverage dynamics that we seek to uncover"- Debt Financing and Financial Flexibility Evidence from Proactive Leverage Increases (David J. Denis and Stephen B. McKeon)
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