Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: st: Why do I get two different results from the same specification and the same dataset?
From
Yuval Arbel <[email protected]>
To
[email protected]
Subject
Re: st: Why do I get two different results from the same specification and the same dataset?
Date
Sun, 6 Nov 2011 20:16:40 +0200
Thanks for your assistance. Indeed there is a mistake:
I mistakenly defined dev_cost_int as dev_cost*area instead of dev_cost*min
Yuval
On Sun, Nov 6, 2011 at 7:03 PM, Richard Williams
<[email protected]> wrote:
> Like everyone else, I strongly suspect you computed the interactions wrong.
> Maybe you accidentally used a wrong variable in the calculation. I would
> especially double-check the calculation of the units interaction, as it is
> by far and away the most different coefficient in your two models: 128,569.4
> in the first model (and highly significant) and -.2338972 (and
> insignificant) in the 2nd. Also the main effect of units switches from large
> positive to large negative.
>
> If you are convinced the coding is right I might try rescaling bid_win, e.g.
> dividing by 1000. Their might be some sort of precision issue.
>
> At 07:24 AM 11/6/2011, Yuval Arbel wrote:
>>
>> Dear statalist participants,
>>
>> when I run the following regression
>>
>> reg bid_win dev_cost bid_num year area units min min_price
>> c.dev_cost#i.min c.bid_num#i.min c.year#i.min c.area#i.min
>> c.units#i.min
>>
>> I get the following output:
>>
>>
>> Source | SS df MS Number of obs =
>> 6802
>> -------------+------------------------------ F( 12, 6789) =
>> 2891.19
>> Model | 7.0107e+17 12 5.8423e+16 Prob > F =
>> 0.0000
>> Residual | 1.3719e+17 6789 2.0207e+13 R-squared =
>> 0.8363
>> -------------+------------------------------ Adj R-squared =
>> 0.8361
>> Total | 8.3826e+17 6801 1.2326e+14 Root MSE =
>> 4.5e+06
>>
>>
>> ------------------------------------------------------------------------------
>> bid_win | Coef. Std. Err. t P>|t| [95% Conf.
>> Interval]
>>
>> -------------+----------------------------------------------------------------
>> dev_cost | -.0782451 .1319286 -0.59 0.553 -.3368666
>> .1803764
>> bid_num | 53637.98 18087.12 2.97 0.003 18181.54
>> 89094.41
>> year | 61991.65 44544.85 1.39 0.164 -25330.21
>> 149313.5
>> area | 204.3705 105.0742 1.95 0.052 -1.607834
>> 410.3488
>> units | 52691.04 11756.39 4.48 0.000 29644.82
>> 75737.26
>> min | 1.04e+08 9.74e+07 1.06 0.288 -8.73e+07
>> 2.95e+08
>> min_price | 3.956053 .0241168 164.04 0.000 3.908777
>> 4.00333
>> |
>> min#|
>> c.dev_cost |
>> 1 | -.460682 .1391518 -3.31 0.001 -.7334631
>> -.187901
>> |
>> min#|
>> c.bid_num |
>> 1 | -43194.68 19552.09 -2.21 0.027 -81522.9
>> -4866.457
>> |
>> min#c.year |
>> 1 | -51639.35 48543.57 -1.06 0.287 -146800
>> 43521.27
>> |
>> min#c.area |
>> 1 | 186.6343 110.1857 1.69 0.090 -29.36416
>> 402.6327
>> |
>> min#c.units |
>> 1 | -128569.4 12642.23 -10.17 0.000 -153352.2
>> -103786.7
>> |
>> _cons | -1.25e+08 8.94e+07 -1.39 0.163 -3.00e+08
>> 5.05e+07
>>
>> ------------------------------------------------------------------------------
>>
>>
>> But when I define directly the interaction variables, and run the
>> regression, I get different outcomes:
>>
>> . reg bid_win dev_cost bid_num year area units min min_price
>> dev_cost_int bid_num_int year_int area_int units_int
>>
>> Source | SS df MS Number of obs =
>> 6802
>> -------------+------------------------------ F( 12, 6789) =
>> 2840.90
>> Model | 6.9905e+17 12 5.8254e+16 Prob > F =
>> 0.0000
>> Residual | 1.3921e+17 6789 2.0505e+13 R-squared =
>> 0.8339
>> -------------+------------------------------ Adj R-squared =
>> 0.8336
>> Total | 8.3826e+17 6801 1.2326e+14 Root MSE =
>> 4.5e+06
>>
>>
>> ------------------------------------------------------------------------------
>> bid_win | Coef. Std. Err. t P>|t| [95% Conf.
>> Interval]
>>
>> -------------+----------------------------------------------------------------
>> dev_cost | .3458744 .1259233 2.75 0.006 .0990254
>> .5927235
>> bid_num | 50612.77 18218.04 2.78 0.005 14899.71
>> 86325.84
>> year | 26138.3 44731.32 0.58 0.559 -61549.1
>> 113825.7
>> area | 796.392 88.98841 8.95 0.000 621.9468
>> 970.8371
>> units | -56322.78 4522.886 -12.45 0.000 -65189.06
>> -47456.51
>> min | 2.11e+07 9.78e+07 0.22 0.829 -1.71e+08
>> 2.13e+08
>> min_price | 3.914549 .0241269 162.25 0.000 3.867252
>> 3.961845
>> dev_cost_int | -.9575921 .1316807 -7.27 0.000 -1.215728
>> -.6994567
>> bid_num_int | -40191.13 19694.51 -2.04 0.041 -78798.54
>> -1583.728
>> year_int | -10450.87 48755.43 -0.21 0.830 -106026.8
>> 85125.05
>> area_int | -443.5883 91.15801 -4.87 0.000 -622.2866
>> -264.89
>> units_int | -.2338972 .131622 -1.78 0.076 -.4919176
>> .0241233
>> _cons | -5.29e+07 8.98e+07 -0.59 0.556 -2.29e+08
>> 1.23e+08
>>
>> ------------------------------------------------------------------------------
>>
>> My question is why do I get two different results from the same
>> specification?
>> Just to exemplify: note that the coefficient of "dev_cost" has
>> modified signs and became significant
>>
>> --
>> Dr. Yuval Arbel
>> School of Business
>> Carmel Academic Center
>> 4 Shaar Palmer Street, Haifa, Israel
>> e-mail: [email protected]
>> *
>> * For searches and help try:
>> * http://www.stata.com/help.cgi?search
>> * http://www.stata.com/support/statalist/faq
>> * http://www.ats.ucla.edu/stat/stata/
>
> -------------------------------------------
> Richard Williams, Notre Dame Dept of Sociology
> OFFICE: (574)631-6668, (574)631-6463
> HOME: (574)289-5227
> EMAIL: [email protected]
> WWW: http://www.nd.edu/~rwilliam
>
> *
> * For searches and help try:
> * http://www.stata.com/help.cgi?search
> * http://www.stata.com/support/statalist/faq
> * http://www.ats.ucla.edu/stat/stata/
>
--
Dr. Yuval Arbel
School of Business
Carmel Academic Center
4 Shaar Palmer Street, Haifa, Israel
e-mail: [email protected]
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/