Re: st: Clarification Re: Stata 13, +

[Lucas <lucaselastic@gmail.com>]

Thanks for the clarifications.  I look forward to 1)ordering stata 13
sometime this week and 2)using the new materials that may be developed
on the multilevel commands.

Thanks again!

On Mon, Jun 10, 2013 at 3:21 PM, Rafal Raciborski, StataCorp
<rraciborski@stata.com> wrote:
> Sam <lucaselastic@gmail.com> has a question about Stata licensing:
>
>> Am I correct in understanding that the perpetual license entails
>> exactly the same terms as before if I do not choose the maintenance
>> option?  Am I correct in understanding that I will be able to update
>> stata (as long as it is still stata 13.x) if I choose not to pay the
>> maintenance option?  Or, am I mistaken, and the maintenance fee is
>> required to "maintain" an up-to-date stata prior to the next major
>> release?
>
> Your understanding is correct.  A perpetual Stata license still works
> exactly
> as it always has, including free updates via the -update- command along
> the
> way, whether you have maintenance or not.  If you have maintenance in
> effect
> and another major version of Stata comes out (i.e. Stata 14), you
> automatically
> receive a new perpetual license to that major version.
>
> Sam also asked about multilevel mixed-effects models where level-2
> variables
> are introduced for level-1 slopes:
>
>> It is great that stata allows users to look through the manual for the
>> new release early.  I did, and found myself wishing for one simple
>> change in the multilevel segment, an addition, really.  Many analysts
>> use the multilevel model to introduce level-2 variables into equations
>> for level-1 slopes.  So, for example, the analyst might add a variable
>> for per pupil expenditure to the model such that it alters the slope
>> for parents' income in a model predicting student test score.
>
> To fit such models in Stata, one needs to translate the multistage
> formulation
> of a mixed-effects model into a one-equation formulation specified for the
> outcome.  For example, consider a two-stage formulation:
>
>   y_ij    = eta_i0 + eta_i1*x_ij + e_ij         (level 1)
>   eta_i0  = b_00 + b_01*z0_i + u_i0             (level-2 intercept)
>   eta_i1  = b_10 + b_11*z0_i + u_i1             (level-2 slope)
>
> which contains one level-1 variable x and one level-2 variable z0,
> which varies at the slope and intercept levels.
>
> To obtain a one-equation formulation, we substitute eta_i0 and eta_i1 into
> the level-1 equation:
>
>   y_ij = (b_00+b_01*z0_i+u_i0) + (b_10+b_11*z0_i+u_i1)*x_ij + e_ij
>         (after rearranging terms)
>        = (b_00 + b_01*z0_i + b_10*x_ij + b_11*z0_i*x_ij)        <-- fixed
>        + (u_i0 + x_ij*u_i1 + e_ij                               <-- random
>
> To fit this model using, for example, -mixed-, we would type
>
>   . mixed y x z0 c.x#c.z0 || id: x
>
> where 'id' is the level-2 identifier, y is the outcome variable, and x and
> z0
> are the corresponding level-1 and level-2 variables.  We assumed that x
> and z0
> are continuous and used the factor notation to include their interaction
> in
> the model.
>
> We will consider including an example of a multistage formulation in our
> documentation.  For more examples, Sam may also look at Rabe-Hesketh &
> Skrondal (2012), for example, chapters 4.9 and 7.4.
>
> --Rafal
> rraciborski@stata.com
>
> References
>
> S. Rabe-Hesketh & A. Skrondal. 2012. Multilevel and Longitudinal Modeling
> using Stata. Stata Press, 3rd edition.
>
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