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From |
Richard Williams <richardwilliams.ndu@gmail.com> |

To |
statalist@hsphsun2.harvard.edu, statalist@hsphsun2.harvard.edu |

Subject |
Re: st: indicator variable and interaction term different signs but both significant |

Date |
Sun, 07 Apr 2013 16:08:29 -0500 |

At 05:21 AM 4/7/2013, Nahla Betelmal wrote:

Thank you all for your valuable comments. It was very interesting to interact with you guys. I think my case is shown in this useful file http://www.sagepub.com/upm-data/21120_Chapter_7.pdf . Figure 7.9, page 134.

Many thanks again Nahla On 7 April 2013 08:25, Richard Williams <richardwilliams.ndu@gmail.com> wrote: > > At 11:07 PM 4/6/2013, David Hoaglin wrote: > >> Richard gave the following interpretation of the coefficient of OC_D >> in the initial model: "The coefficient for OC-D is the predicted >> difference between an overconfident manager and a regular manager when >> MV = 0 and the values of other variables are the same for both." The >> phrase "and the values of other variables are the same for both," >> however, does not reflect the way multiple regression works. The >> appropriate general interpretation of an estimated coefficient is that >> it tells how the dependent variable changes per unit change in that >> predictor after adjusting for simultaneous linear change in the other >> predictors in the data at hand. (I realize that various books have >> interpretations similar to the one that Richard gave, but that does >> not make those interpretations correct in general.) Since OC_D is an >> indicator variable, its coefficient gives the difference, on average, >> between overconfident managers and rational managers after adjusting >> for the contributions of the other predictors. One of those other >> predictors is OC_MV, so the resulting interpretation for the >> coefficient of OC_D is the one that I gave above. > >> I have to admit that I don't understand what is wrong with mystatement, at least in the case of this specific example. To beclear, if MV = 0, the interaction term OC_MV will also equal 0. So,go ahead and plug in whatever values you want for the othervariables, compute the predicted values for a regular manager andan overconfident manager, and it will indeed always be the casethat "The coefficient for OC_D is the predicted difference betweenan overconfident manager and a regular manager when MV = 0 and thevalues of other variables are the same for both." They have to besince the calculations of the predicted values are identical forboth, except that for regular managers the coefficient for OC_Dgets multiplied by 0 whereas for overconfident managers it getsmultiplied by 1.>> I would agree that things like other interaction terms or X^2terms make life more complicated, e.g. two cases can't havedifferent values of X while having the same value of X^2. But, thatisn't the case here. I also don't think it makes much sense in sucha case to talk about the effect of X separate from the effect ofX^2, so I am not clear how the language on "after adjusting forsimultaneous linear change in the other predictors at hand" reallyhelps any. Even if it were more technically correct, I don't thinkit is at all clear what it means. You have to break down and use afew sentences when you have interaction terms and squared terms andthings like that!> > > > ------------------------------------------- > Richard Williams, Notre Dame Dept of Sociology > OFFICE: (574)631-6668, (574)631-6463 > HOME: (574)289-5227 > EMAIL: Richard.A.Williams.5@ND.Edu > WWW: http://www.nd.edu/~rwilliam > > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/faqs/resources/statalist-faq/ > * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/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: Richard.A.Williams.5@ND.Edu WWW: http://www.nd.edu/~rwilliam * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**References**:**st: indicator variable and interaction term different signs but both significant***From:*Nahla Betelmal <nahlaib@gmail.com>

**Re: st: indicator variable and interaction term different signs but both significant***From:*Anthony Fulginiti <fulginit@usc.edu>

**Re: st: indicator variable and interaction term different signs but both significant***From:*Nahla Betelmal <nahlaib@gmail.com>

**Re: st: indicator variable and interaction term different signs but both significant***From:*Richard Williams <richardwilliams.ndu@gmail.com>

**Re: st: indicator variable and interaction term different signs but both significant***From:*Nahla Betelmal <nahlaib@gmail.com>

**Re: st: indicator variable and interaction term different signs but both significant***From:*David Hoaglin <dchoaglin@gmail.com>

**Re: st: indicator variable and interaction term different signs but both significant***From:*Richard Williams <richardwilliams.ndu@gmail.com>

**Re: st: indicator variable and interaction term different signs but both significant***From:*Nahla Betelmal <nahlaib@gmail.com>

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