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Re: st: Running Product Function


From   Yuval Arbel <yuval.arbel@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Running Product Function
Date   Mon, 10 Dec 2012 00:25:03 +0200

Thanks Nick. That was very helpful.

On Mon, Dec 10, 2012 at 12:14 AM, Yuval Arbel <yuval.arbel@gmail.com> wrote:
> Note also that the geometric mean of this series is 25. This implies
> that while the arithmetic mean gives more weight to earlier periods,
> the geometric mean gives more weight to latter periods.:
>
>  ameans(reduct_per)if appt==2862
>
>     Variable |    Type        Obs        Mean       [95% Conf. Interval]
> -------------+----------------------------------------------------------
>   reduct_per | Arithmetic      37    8.108108        4.152295   12.06392
>              |  Geometric      12          25              25         25
>              |   Harmonic      12          25              25         25
> ------------------------------------------------------------------------
>
>
>
> On Mon, Dec 10, 2012 at 12:06 AM, Yuval Arbel <yuval.arbel@gmail.com> wrote:
>> Eventually, I improved the system and put:the following commands:
>>
>> by appt: replace reduct_per=1 if reduct_per==0
>> by appt: gen y1=exp(sum(ln(reduct_per)))
>>
>> I got the following table, which is exactly what I need (I don't want
>> the geometric mean to be set to zero):
>>
>> . list reduct_per y3 if appt==2862
>>
>>         +---------------------+
>>         | reduct~r         y3 |
>>         |---------------------|
>>     30. |        1          1 |
>>     31. |        1          1 |
>>     32. |        1          1 |
>>     33. |        1          1 |
>>     34. |        1          1 |
>>         |---------------------|
>>     35. |        1          1 |
>>     36. |        1          1 |
>>     37. |        1          1 |
>>     38. |        1          1 |
>>     39. |        1          1 |
>>         |---------------------|
>>     40. |        1          1 |
>>     41. |        1          1 |
>>     42. |        1          1 |
>>     43. |        1          1 |
>>     44. |        1          1 |
>>         |---------------------|
>>     45. |        1          1 |
>>     46. |        1          1 |
>>     47. |        1          1 |
>>     48. |        1          1 |
>>     49. |        1          1 |
>>         |---------------------|
>>     50. |        1          1 |
>>     51. |        1          1 |
>>     52. |        1          1 |
>>     53. |        1          1 |
>>     54. |        1          1 |
>>         |---------------------|
>>     55. |       25         25 |
>>     56. |       25        625 |
>>     57. |       25      15625 |
>>     58. |       25     390625 |
>>     59. |       25    9765625 |
>>         |---------------------|
>>     60. |       25   2.44e+08 |
>>     61. |       25   6.10e+09 |
>>     62. |       25   1.53e+11 |
>>     63. |       25   3.81e+12 |
>>     64. |       25   9.54e+13 |
>>         |---------------------|
>>     65. |       25   2.38e+15 |
>>     66. |       25   5.96e+16 |
>>         +---------------------+
>>
>>
>> On Sun, Dec 9, 2012 at 11:56 PM, Nick Cox <njcoxstata@gmail.com> wrote:
>>> That is reasonable if and only if zero is in effect a code for missing
>>> in your situation.
>>>
>>> (In terms of your earlier reference, -prod()- is a user-written -egen-
>>> function which must be installed from
>>>
>>> STB-51  dm71  . . . . . . . . . . . .  Calculating the product of observations
>>>         (help prod if installed)  . . . . . . . . . . . . . . . . . .  P. Ryan
>>>         9/99    pp.3--4; STB Reprints Vol 9, pp.45--48
>>>         extension to egen for producing the product of observations
>>>
>>> Please remember to explain _where_ you obtained user-written code.)
>>>
>>> Nick
>>>
>>> On Sun, Dec 9, 2012 at 9:40 PM, Yuval Arbel <yuval.arbel@gmail.com> wrote:
>>>> I don't have negative values, but I have zeros, in which case I can
>>>> replace them by one and then take the -ln()-
>>>>
>>>> On Sun, Dec 9, 2012 at 11:31 PM, Nick Cox <njcoxstata@gmail.com> wrote:
>>>>> Oddly enough I was thinking earlier today about how you would
>>>>> generalise this if any values were not positive.
>>>>>
>>>>> If any value is zero, then the product becomes zero; otherwise one
>>>>> would need to separate out products of -abs()- and -sign()-.
>>>>>
>>>>> Nick
>>>>>
>>>>> On Sun, Dec 9, 2012 at 9:19 PM, Yuval Arbel <yuval.arbel@gmail.com> wrote:
>>>>>
>>>>>> Please ignore my previous e-mails regarding this question
>>>>>>
>>>>>> After a short additional search, I found a very nice (and well known)
>>>>>> trick proposed by Nick Cox to address the problem (which, from some
>>>>>> reason did not come to my mind):
>>>>>>
>>>>>> bysort group : gen prod = sum(ln(x))
>>>>>> by group : replace prod = exp(prod[_N])
>>>>>>
>>>>>> On Sun, Dec 9, 2012 at 11:05 PM, Yuval Arbel <yuval.arbel@gmail.com> wrote:
>>>>>>> P.S. According to stata's help, the details of the author of the
>>>>>>> -prod()- function is:
>>>>>>>
>>>>>>> Philip Ryan
>>>>>>> Department of Public Health
>>>>>>> University of Adelaide
>>>>>>> South Australia
>>>>>>> pryan@medicine.adelaide.edu.au
>>>>>
>>>>>
>>>>> On Sun, Dec 9, 2012 at 10:53 PM, Yuval Arbel <yuval.arbel@gmail.com> wrote:
>>>>>
>>>>>>>> I appreciate very much your assistance in the following question:,
>>>>>>>>
>>>>>>>> I'm looking for an equivalent function for -gen y1=sum()- which will
>>>>>>>> calculate running product for each point in time
>>>>>>>>
>>>>>>>> In fact, what I would like to calculate is a running geometric mean
>>>>>>>>
>>>>>>>> Note also that -gen y2=prod()- does not work (i.e., stata does not
>>>>>>>> identify the function). Only -egen y2=prod()- works, but it generates
>>>>>>>> only one product for each panel, and this is not what I need.
>>>>>>>>
>>>>>>>> Finally, I tried the -amean- command,, but it simply gives summary
>>>>>>>> statistics of different means, and it is not a function..
>>> *
>>> *   For searches and help try:
>>> *   http://www.stata.com/help.cgi?search
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>>> *   http://www.ats.ucla.edu/stat/stata/
>>
>>
>>
>> --
>> Dr. Yuval Arbel
>> School of Business
>> Carmel Academic Center
>> 4 Shaar Palmer Street,
>> Haifa 33031, Israel
>> e-mail1: yuval.arbel@carmel.ac.il
>> e-mail2: yuval.arbel@gmail.com
>
>
>
> --
> Dr. Yuval Arbel
> School of Business
> Carmel Academic Center
> 4 Shaar Palmer Street,
> Haifa 33031, Israel
> e-mail1: yuval.arbel@carmel.ac.il
> e-mail2: yuval.arbel@gmail.com



-- 
Dr. Yuval Arbel
School of Business
Carmel Academic Center
4 Shaar Palmer Street,
Haifa 33031, Israel
e-mail1: yuval.arbel@carmel.ac.il
e-mail2: yuval.arbel@gmail.com
*
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