Hello everyone, assuming my regression is
Code:
areg roa c.ownership##c.ownership leverage firmage firmsize, a(firm)
, which shows there is a non-linear relation between roa and ownership.

How can I plot a quadratic line between roa and ownership while controlling all the rest variables constant at their means? I found some options from graph - twoway, but it seems only predict the relation between roa and ownership without considering the impact of other variables

Thanks for any comment

Code:
* Example generated by -dataex-. For more info, type help dataex
clear
input long firm double(roa leverage firmage firmsize ownership)
 4    .05787033623352358  .4607225863260322  2.772588722239781 19.218227600266285               .5232
 4     .0321234965736189  .4601395135252982 2.8903717578961645  19.28725653955515   .5236000000000001
 4   -.11918624495170212  .3588437880368989  2.995732273553991   18.9630199009463  .47929999999999995
 4    .01495393978372191  .4504149833158276  3.044522437723423 19.135122760068622               .3672
 4   -.06843544150433355  .4917934111961387 3.1354942159291497   18.9630199009463               .2608
 4   .019662891675855866  .6103675476223739 3.1780538303479458 19.255813734390493                   0
 4   .046830003727583745  .2949351535993749  3.258096538021482 19.095191436359503                   0
 4    .04050635388779153  .2325276091520232  3.295836866004329 19.077752816822542                   0
 4   .023938467922043048  .4032394211408936  3.332204510175204  19.30507651488318                   0
 4   .046188643554358366  .5347544682054719  3.367295829986474 19.639392142978075                   0
 4    .01719991819670127  .5904017152495257 3.4011973816621555 19.803653362037466                   0
 4     .1775298333690193 .20345630761888872  3.433987204485146  19.22588925800566 .009300000000000001
 4    .02191692926187318 .31524660751399686  3.433987204485146 19.409642943364215                   0
 4  -.061543475694888994  .4779659365925319  3.433987204485146  19.67680226667089                   0
 4 -.0024115198348312527  .0602434295383638  3.433987204485146 21.125051026612525                   0
 5   -.03745258992845414  .4329653499047152 2.4849066497880004  21.37783590458201               .0625
 5  .0005171686877404424 .47957627696477384 2.6390573296152584  21.30032987497388               .0625
 5  .0009335747688180074  .5093521462642073   2.70805020110221 21.316929617074006               .0625
 5   -.10947926941264176  .5983874198978687  2.772588722239781  21.22032107153577               .0625
 5   .035869482949014195  .5408640835784261  2.833213344056216  21.14741778140122                .043
 5   .053104612201860295  .4850050686292299 2.8903717578961645 21.099661757017564                .042
 5   .007559023553588451 .45864512288376236 2.9444389791664403  21.05187239719703               .0364
 5   -.03708261410159387  .4675749549866466  2.995732273553991  21.00029428216922               .0364
 5  -.003421735983836361  .4779603182432544  3.044522437723423 20.980701515308343               .0364
 5    .00905503454132357  .4764843410624268  3.091042453358316  20.95484265861465               .0364
 5   .016686805744591075   .483141538409433 3.1354942159291497 21.000672107227555               .0364
 5  -.035624123614119804  .4748309447752741 3.1780538303479458  20.89608736871081               .0364
 5    .03158343984215735  .5099635880102232 3.2188758248682006  21.03563843017662               .0364
 5  -.024626937110126847 .44703998898092584  3.258096538021482  21.50899620535022               .0288
 5    .04628077822456593 .46370847966123363  3.295836866004329  21.65039180470303               .0288
 5   .007876100430552625  .5177473589674079  3.332204510175204 21.792140301952397               .0155
 5   .050217034684912974 .49403993639847327  3.367295829986474 21.861554945892184                   0
 5   .058874672135832556 .42533743759104903 3.4011973816621555 21.832435854914394               .0088
 6   .036033819874841805  .6663128608340783 2.4849066497880004 22.055054167952534               .2839
 6    .03137663053046068  .6840094020756348 2.5649493574615367  22.16284912999035               .2839
 6   -.07754126498152206  .7276308729960651   2.70805020110221 22.101588925663833                .285
 6    .01213039737059797  .7189990036601428  2.772588722239781 22.114683010213927               .2839
 6    .04082244446876744  .5575793748960657  2.833213344056216 21.660563172367947               .2839
 6    .07381351515660856    .54558160744419 2.8903717578961645 21.794481355021016               .2162
 6    .04532762424723061  .6774184371510349 2.9444389791664403 22.440379192654035  .20170000000000002
 6   .025367310959577047  .7166751445693527  2.995732273553991  22.50184589296331               .1965
 6    .04609759347852708  .6985768064896655  3.044522437723423  22.70730098027619  .18760000000000002
 6   .057942059022990655  .7014206033085816  3.091042453358316 22.871335447618527               .2574
 6    .05216514790634165  .6528552397639044 3.1354942159291497 22.842165330871687               .2574
 6    .06738054038720612  .6201650001341875 3.1780538303479458  22.95793928724029  .26680000000000004
 6    .07002386641567787  .5799717502905758 3.2188758248682006 23.022661852734036  .30379999999999996
 6    .04360112953523529  .6414202485779869  3.258096538021482 23.187392871472024  .34509999999999996
 6   .034540541559403316  .6461507723496202  3.295836866004329  23.26514371434046               .3751
 6    .06103667380740991  .6104992056557073  3.332204510175204  23.30123662561863               .3751
 6    .06244191741112164  .5656477276222713  3.367295829986474 23.298921622382668               .3751
 6    .06819427734297234  .5282362718093485 3.4011973816621555  23.32867243452097  .40509999999999996
 6    .05354384054264582  .5446121032519958  3.433987204485146   23.4798090692308               .4059
 7    -.1876207447354162  .8550579006279933 2.5649493574615367  20.67395924097653               .3296
 7   .011558831482141015   .829789863944599 2.6390573296152584 20.820550034340794               .3297
 7   .014203391636424765  .7634611673488952  2.772588722239781 20.834524686173463 .049699999999999994
 7    -.1472548268373538  .9092556112753906  2.833213344056216  20.77055036557721 .049699999999999994
 7   .012049352855845335  .8729908432673958 2.8903717578961645 20.565779312009504 .049699999999999994
 7   -.12364768107203755  .9787454482313142 2.9444389791664403 20.507442411057877 .038599999999999995
 7    .01177949227374375  1.011333903766873  2.995732273553991  20.41834662505445                   0
 7   -.10645577219450246 1.1226146881264438  3.044522437723423  20.23003515965535                   0
 7    .05621334127464616 1.1498988601543951  3.091042453358316 19.710661293610627                   0
 7    .06527903160641156  1.098531029043014 3.1354942159291497 19.621914504791228                   0
 7   .022930988812767884 .19342039413519121 3.1780538303479458 19.708301040554044                   0
 7   .005614041578245276  .6241584231498458 3.2188758248682006  20.48713836630509                   0
 7   .028639181838631657 .46275425805767784  3.258096538021482 20.303973452300507 .050100000000000006
 7  -.049025421173671084  .4742943653974571  3.295836866004329 20.338963088573255               .0195
 7   .027560054552458434 .22384748126113732  3.332204510175204  19.99005577851841                 .01
 7     .1585790901726705  .1499620643710975  3.367295829986474   20.0584489277492                   0
 7  .0017960226238898176 .11802889574425025 3.4011973816621555 19.908347763948512                   0
 7    -.3601920345168437  .6434306664550695  3.433987204485146 20.115764092598607                   0
 7   .041651386601188126  .6012610560101671  3.433987204485146 20.095332113871997                   0
 9   .014174241181624888  .6786233468928654 2.4849066497880004 22.121045561334835               .2279
 9   .008418301990424284   .691097729198897 2.5649493574615367 22.136795228936446               .1115
 9   .023321415043949564  .6498250993938895  2.772588722239781 22.310075256228277               .1116
 9     .0284333842103851   .646418839799356  2.833213344056216 22.430015974029505               .1115
 9   .056781033676623086  .5912805988392213 2.8903717578961645  22.48787671621316               .1115
 9    .04463417243585205  .5899988771702805 2.9444389791664403  22.52889364723692               .0695
 9    .05446466053939489  .6020921099241675  2.995732273553991  22.73843677607795               .0678
 9    .04405083092833007   .629529979089809  3.044522437723423 23.028312678498494  .08070000000000001
 9    .03227960025216681  .6504021055512751  3.091042453358316 23.190146785426087               .0623
 9    .02333106279716629  .6436690392861527 3.1354942159291497  23.30130833247465               .0623
 9    .03262986444719718  .6287977618807954 3.1780538303479458  23.33420300252358               .0623
 9    .03209050794474974  .6289341671336012 3.2188758248682006 23.412846220969694               .0623
 9   .053323504502728505  .6382021174383912  3.258096538021482  23.61994726945558               .0557
 9   .019399877156343247  .6237910675039087  3.295836866004329 23.797019970306426               .0557
 9   .011923784396394046  .6331205554612953  3.332204510175204 24.023148762531836               .0557
 9   .022280568703266983  .6498955892815201  3.367295829986474 24.119444013660647               .0557
 9   .023563756371373736  .6455591121139688 3.4011973816621555 24.131432397235574               .0557
10   .043489349330943755  .6021208666376154  2.772588722239781  20.58029715300303               .2062
10    -.2338764404240956  .7912486608797766 2.8903717578961645   19.6832583891498               .2062
10    .04153607427746676  .6386542830331817  3.091042453358316 19.261623544009687               .2062
10   .018060520974888063  .5974202642586004 3.1354942159291497 19.173046549814014               .2062
10   .014986191541823363  .6022387853497403 3.2188758248682006  19.29523169910633               .2062
10  .0037077236091027977  .3581516419214527  3.258096538021482 20.750676322926644  .09160000000000001
10   -.09365409043696454 .31412842340973274  3.295836866004329 20.505381472346333               .0638
10  .0038693136262392333  .5795766968251589  3.332204510175204 22.364625370313675                 .06
10   .008022458238600682  .5447209317979287  3.367295829986474 22.302922166104075                 .06
10    -.3381495394535607  .6201161017598043 3.4011973816621555 21.856328843229758               .0535
10   -.22195259878634666  .8195049001496428  3.433987204485146  21.90905785706952               .0535
10   .029388978524123463  .8243732730012927  3.433987204485146 22.179939449414093               .0535
end