Re: st: predicting height by age for each individual

["Y.R.E. Retamal" <yrer2@cam.ac.uk>]

Dear Maarten

Thank you very much for your comments. I know that height do not change 
linearly with age, I just put this equation to simplify my question. My 
question is more related to automatize regressions (and their 
predictions) than the equation itself. Nevertheless, thank you very much 
for your advice
Concerning your second comment, I am sorry, I committed a mistake. I 
wanted to put: predict xb if id==1. Thus, the predicted values will be 
filled just in the cells associated to id 1. Problems begin from the 
second individual (id 2), because xb is already defined. So, I would 
have to put a different name to variable xb for id==2, e.g. xb2, which 
will have non missing values just for id==2. After that:

replace xb=xb2 if id==2
drop xb2

putting the predicted values for id==1 and id==2 in just one variable.
I would like to automatize all this procedure.
I hope have been clearer

Rodrigo


On 2014-01-30 15:47, Maarten Buis wrote:
> I have two comments:
>
> As a father I can tell you that height does not change linearly with
> age in that period. You might want to look at -fp- in order to create
> a reasonable model.
>
> Imangine what happens in your code when you have three persons. Your
> first regression will fill in for person 2 and 3, your second
> regression will be used to fill in 1 and 3, but wait.. you already
> filled in for person 3. What do you want to do in that case?
>
> -- Maarten
>
>
> On Thu, Jan 30, 2014 at 4:26 PM, Y.R.E. Retamal <yrer2@cam.ac.uk> 
> wrote:
> > Dear STATA users
> >
> > I am studying growth and development in children from 0 to 3 years 
> > old. I am
> > using a longitudinal database of children where height and weight were
> > measured from birth to three years old (1600 children).
> > I would like to predict height of each child from birth until three 
> > years
> > old for each six months (birth, 6, 12, 18, ..., 36 month), after 
> > running a
> > linear regression of height by age for each child, not all at the same 
> > time.
> > For example, I have the following database:
> >
> > id      month   height
> > 1       0       59
> > 1       6       68
> > 1       12      70
> > 1       18      74
> > 1       24      81
> > 1       30      86
> > 1       36      94
> > 2       0       50
> > 2       6       55
> > 2       12      74
> > 2       18      80
> > 2       24      82
> > 2       30      87
> > 2       36      95
> >
> >
> > I could do:
> > reg height month if id==1
> > predict xb if id!=1
> > reg height month if id==2
> > predict xb if id!=2
> >
> > and so...
> >
> > But, I have 1600 children, therefore I should write the same commands 
> > per
> > each child (1600 times), something truly inefficient and tedious. 
> > There is a
> > command or program to run the same commands, but automatically?
> >
> >
> > Any help would be very appreciated.
> > Rodrigo
> >
> > *
> > *   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/
>
>
>
> --
> ---------------------------------
> Maarten L. Buis
> WZB
> Reichpietschufer 50
> 10785 Berlin
> Germany
>
> http://www.maartenbuis.nl
> ---------------------------------
> *
> *   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/