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RE: st: Estimating Logit Price Response Function With Unknown Market Size


From   "Marigliano, Joseph" <JMarigliano@premierfarnell.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Estimating Logit Price Response Function With Unknown Market Size
Date   Tue, 3 Dec 2013 11:27:46 -0600

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: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox
Sent: Wednesday, November 27, 2013 1:12 PM
To: statalist@hsphsun2.harvard.edu
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
njcoxstata@gmail.com


On 27 November 2013 15:47, Marigliano, Joseph
<JMarigliano@premierfarnell.com> 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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