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Re: st: Estimating Logit Price Response Function With Unknown Market Size
From
Nick Cox <[email protected]>
To
"[email protected]" <[email protected]>
Subject
Re: st: Estimating Logit Price Response Function With Unknown Market Size
Date
Tue, 3 Dec 2013 17:40:25 +0000
What's holding you back? You can try it yourself and see.
input Price Cumulative
<your data>
nl log3 C P
predict predicted
twoway connected C P || line predicted P, sort
Answer: not too bad, gets it wrong for high prices.
Nick
[email protected]
On 3 December 2013 17:27, Marigliano, Joseph
<[email protected]> wrote:
> Nick, thanks. I have taken a look.
> Here is the example data:
>
> Price Cummulative Quantity
> 0.1 8100
> 0.2 8000
> 0.3 7800
> 0.4 7500
> 0.5 6700
> 0.6 5700
> 0.7 4000
> 0.8 2500
> 0.9 1200
> 1 700
> 1.1 500
> 1.2 400
> 1.3 350
> 1.4 300
> 1.5 290
>
> I am trying to fit this as a Reverse Sigmoid curve. Will nl log3 still
> be appropriate in this case?
>
> Regards,
>
> Joseph
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Nick Cox
> Sent: Wednesday, November 27, 2013 1:12 PM
> To: [email protected]
> Subject: Re: st: Estimating Logit Price Response Function With Unknown
> Market Size
>
> You asked the same question on 22 November.
>
> When there is no response, often a question is perceived as not being
> clear enough to answer.
>
> I read this as fitting a logistic growth curve to time series. The upper
> asymptote is unknown and thus a parameter to be estimated. This is a
> classic for -nl-: indeed a sample program -log3- for precisely this
> model is bundled with Stata. Have look at the manual entry for -nl-.
>
> Nick
> [email protected]
>
>
> On 27 November 2013 15:47, Marigliano, Joseph
> <[email protected]> wrote:
>
>> I have a file containing historical sales data by product.
>> It contains product and cumulative sales by price point for the last 6
>
>> months.
>> I am looking to estimate the curve as a logit, but do not know the
>> market size.
>> Are there any good examples of this?
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