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Re: AW: st: prgen option quadratic term

From   Nick Cox <>
Subject   Re: AW: st: prgen option quadratic term
Date   Wed, 7 Nov 2012 10:42:06 +0000

When you are fitting a linear term and a quadratic term, the two act
together. It's their combined effect that you need to interpret. This
is usually easier with a graph. For example, one negative coefficient
and one positive coefficient mean a turning point somewhere, but not
necessarily within the range of the data.


On Wed, Nov 7, 2012 at 10:35 AM, Meulemann  Max <> wrote:
> thx, the margins and marginsplot function helped a lot.
> Anyways anybody got a idea how I am to interpret my data here: I find a negativ linear term for capitagdp, but if i include a quadratic gdp term, that one turns out to be positiv and significant with a lrtest.
> Plotting with marginsplot tells me then that for the linear model the probability to agree with a certain issue decreases whereas it increases with capitagdp for the quadratic model, keeping fixed my other covariates
> ________________________________________
> Von: []&quot; im Auftrag von &quot;Maarten Buis []
> Gesendet: Dienstag, 6. November 2012 17:10
> An:
> Betreff: Re: AW: st: prgen option quadratic term
> Also see: <>
> -- Maarten
> On Tue, Nov 6, 2012 at 4:26 PM, Richard Goldstein
> <> wrote:
>> I am not familiar with prgen
>> sounds like you want the -margins- command?
>> On 11/6/12 10:24 AM, Meulemann Max wrote:
>>> I d like to get the predicted probabilites as my contionus predicator changes keeping fixed the other ones as it is done in -prgen- only with a quadratic term of that predicator. I do not just want the predicted probabilites.
>>> ________________________________________
>>> Von: []&quot; im Auftrag von &quot;Richard Goldstein []
>>> Gesendet: Dienstag, 6. November 2012 16:10
>>> An:
>>> Betreff: Re: st: prgen option quadratic term
>>> I don't understand; why don't you start by telling us what is wrong with
>>> just using -predict- after your -ologit-? for help on this, start with
>>> -h ologit-, then click on "also see" and click on "ologit postestimation"
>>> Rich
>>> On 11/6/12 10:07 AM, Meulemann Max wrote:
>>>> I would like to calculate predicted probabilities in an ordinal model, ologit or oprobit. I am using a continous quadratic term, which makes calculating the predicted probablities more cumbesome. I am using stata 12
>>>> I found an old entry in the statalist archive that  proposed oprobpr which does work. I was wondering if another package has been written since 2005.
>>>> oprobpr does work, but some of it its features are a bit irritating like how it saves the predicted probailites in another dataset and so on. The nicest way would be to change prgen and its familiar option in a way that the same feature that works for oprobpr would work for prgen.
>>>> the level options allows oproppr to vary an otherwise fixed covariate with a squared term, which is not possible for the x option of prgen.

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