Re: st: Re: [question on -gammafit- and -pgamma-]

[Nick Cox <njcoxstata@gmail.com>]

It's standard that not everything that could be saved is saved,
notably not whatever can be calculated easily from what is saved.

You will need to calculate the intervals yourself using the e(class)
results, e.g.

matrix V = e(V)
di e(alpha) + invnormal(.975) * sqrt(V[1,1])
di e(alpha) - invnormal(.975) * sqrt(V[1,1])

although in your case you want to put results in another matrix, not
-display- them.

Nick

On Sun, Mar 6, 2011 at 8:57 PM, Peter Maclean <pmaclean2011@yahoo.com> wrote:

> When you use -level option you get specific lower and upper limits of the
> coefficients. However, the
>
> e(b) matrix saves only the coefficients. I need confidence intervals for
> different levels of significance and save the results in a matrix for simulation
> purposes. How do you actually do that?
>
> ----- Original Message ----
> From: Nick Cox <njcoxstata@gmail.com>
>
> You need [] not () before the equals sign  in commands like
>
>   matrix results(`i',2)=e(beta)
>
> i.e.
>
>   matrix results[`i',2]=e(beta)
>
> This was explicit in my first email and is explicit in the help for -matrix-.
>
> You have to get used to copying syntax exactly, character by
> character, until you have learned it!
>
> Nick
>
> On Sun, Mar 6, 2011 at 5:36 AM, Peter Maclean <pmaclean2011@yahoo.com> wrote:
>> I made the changes but there are still some errors.
>>
>> for:
>>
>> matrix results=J(10,3,.)
>> egen group = group(n)
>> su group, meanonly
>> forval i = 1/`r(max)' {
>> gammafit y if group == `i'
>>   results(`i',1)=e(alpha)
>>   results(`i',2)=e(beta)
>>   results(`i',3)=e(alpha)*e(beta)
>> }
>>  gives:
>> unrecognized command: results
>> r(199);
>>
>>
>> For:
>>
>> matrix results=J(10,3,.)
>> egen group = group(n)
>> su group, meanonly
>> forval i = 1/`r(max)' {
>> gammafit y if group == `i'
>>   matrix results(`i',1)=e(alpha)
>>   matrix results(`i',2)=e(beta)
>>   matrix results(`i',3)=e(alpha)*e(beta)
>> }
>>
>> gives:
>>
>> invalid syntax
>> r(198);
>>
>>
>>
>> ----- Original Message ----
>> From: Kieran McCaul <Kieran.McCaul@uwa.edu.au>
>
>>
>> (1) get rid of the comma after the gammafit and put the -if- on the same line.
>>     gammafit y if group == `i'
>> (2) the matrix "results" is not the same as the matrix "Results".  Pick one
>>name
>> or the other.
>> (3) You need to preface the matrix assignments with the command -matrix-.
>>
>> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Peter Maclean
>>
>> I tried use the following commnds:
>>
>> matrix results=J(10,3,.)
>> egen group = group(n)
>> su group, meanonly
>> forval i = 1/`r(max)' {
>>   gammafit y,
>>     if group == `i'
>>     Results(`i',1)=e(alpha)
>>     Results(`i',2)=e(beta)
>>     results(`i',3)=e(alpha)*e(beta)
>> }
>>
>> I am still getting the following error
>>
>> { required
>> r(100); and it the results is for all observations.
>
>> ----- Original Message ----
>> From: Nick Cox <njcoxstata@gmail.com>
>>
>> Start with
>>
>> -help foreach-
>>
>> -help forval-
>>
>> If necessary, continue with
>>
>> SJ-2-2  pr0005  . . . . . .  Speaking Stata:  How to face lists with fortitude
>>         . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
>>         Q2/02  SJ 2(2):202--222                                (no commands)
>>         demonstrates the usefulness of for, foreach, forvalues, and
>>         local macros for interactive (non programming) tasks
>>
>> FAQ    . . . . . . . . . . Making foreach go through all values of a variable
>>         . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
>>         8/05    Is there a way to tell Stata to try all values of a
>>                 particular variable in a foreach statement without
>>                 specifying them?
>>                 http://www.stata.com/support/faqs/data/foreach.html
>>
>> On Sat, Mar 5, 2011 at 10:25 PM, Peter Maclean <pmaclean2011@yahoo.com> wrote:
>
>>> Thanks Nick.
>>> My question was actually setting up a loop over a group and save the results.
>>> The number of group (n) is 600.
>>> Hope you can help on that.
>>>
>>> ----- Original Message ----
>>> From: Nick Cox <njcoxstata@gmail.com>
>>>
>>> It is always helpful to specify a subject for your email.
>>>
>>> This question refers to -gammafit- and -pgamma- from SSC, which are
>>> user-written programs.
>>> Statalist etiquette is to explain where user-written programs referred
>>> to come from.
>>>
>>> Peter quotes the syntax
>>>
>>> by n:gammafit y, level(95)
>>>
>>> which -gammafit- supports. However, as is standard with -by:- support,
>>> this syntax is of limited use for _saving_ results, as after the
>>> first, each invocation of -gammafit- stomps over the previous set of
>>> saved results, so although parameter estimates are displayed in turn,
>>> only the last such set is present in memory once all are done.
>>>
>>> Peter correctly reports that -pgamma- does not support the -by()-
>>> option (nor does it support the -by:- prefix).
>>>
>>> I am not aware that Stata supports doubly subscripted variables.
>>> Perhaps Peter means a Stata or Mata matrix.
>>>
>>> To get results for different groups and put them together, Peter has
>>> to arrange that himself. But this code shows that the steps are
>>> simple.
>>>
>>> sysuse auto, clear
>>> matrix results = J(2,2,.)
>>> gammafit mpg if foreign
>>> matrix results[1,1] = e(alpha)
>>> matrix results[1,2] = e(beta)
>>> pgamma mpg if foreign, gen(tp1 ep1)
>>> gammafit mpg if !foreign
>>> matrix results[2,1] = e(alpha)
>>> matrix results[2,2] = e(beta)
>>> pgamma mpg if !foreign, gen(tp2 ep2)
>>> matrix rownames results = Foreign Domestic
>>> matrix colnames results = alpha beta
>>> matrix li results
>>> scatter tp1 ep1 || scatter tp2 ep2 , legend(order(1 "Foreign" 2 "Domestic"))
>>>
>>> For a group variable with many more than 2 classes, it would be better
>>> to set up a loop over the groups.
>>>
>>> The help for -gammafit- includes a link to the help for -maximize-,
>>> which explains how to set initial values.
>>>
>>> Nick
>>>
>>> On Sat, Mar 5, 2011 at 4:47 PM, Peter Maclean <pmaclean2011@yahoo.com> wrote:
>>>
>>>> I am new is Stata modelling.
>>>> I am running the following model:
>>>>
>>>> by n:gammafit y, level(95)
>>>> pgamma y, gen(g_p e_p)
>>>>
>>>> where n is  a group variable.
>>>> I would like to save the estimated parameters by gammafit
>>>>(alpha,beta,alpha+beta
>>>> and lower and upper limit of both alpha and beta) in a variable
>> 'result(n,j).'
>>>>
>>>>
>>>> Also, I would like pgamma to estimate the probabilities (g_p and e_p) by
>>>> variable n.
>>>> The pgamma module does not accept the 'by' option. In addition, is there a
>> way
>>>> to give starting values for the gammafit module?
>

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