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Re: st: RE: generating annualized standard deviation of returns from monthly data.


From   "Ikechukwu M." <bigdoctor2004@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: generating annualized standard deviation of returns from monthly data.
Date   Thu, 27 Feb 2014 11:56:48 -0500

Thank you.

here is what I get when I perform either of the two commands.

I agree that without the year grouping variable there should be one sd
returned per firm. It is including the year grouping variable that
messes things up.


        year              tic            return                sd_return
78. 31jan2000      0183B   -10.71428571          .
79.  29feb2000      0183B             48          .
80.  31mar2000      0183B   -29.72972973          .
------------------------------------------------
81.  30apr2000      0183B    7.692307692          .
82.  31may2000      0183B   -17.85714286          .
83.  30jun2000      0183B    39.13043478          .
84.  31jul2000      0183B         -18.75          .
85.  31aug2000      0183B    61.53846154          .
------------------------------------------------
86.  30sep2000      0183B   -33.33333333          .
87.  31oct2000      0183B    14.28571429          .
88.  30nov2000      0183B         -18.75          .
89.  31dec2000      0183B   -7.692307692          .
90.  31jan2001      0183B           37.5          .
------------------------------------------------
91.  28feb2001      0183B   -27.27272727          .
92.  31mar2001      0183B             50          .
93.  30apr2001      0183B   -18.22222222          .
94.  31may2001      0183B             25          .
95.  30jun2001      0183B   -6.086956522          .
------------------------------------------------
96.  31jul2001      0183B   -20.83333333          .
97.  31aug2001      0183B    2.339181287          .
98.  30sep2001      0183B   -22.85714286          .
99.  31oct2001      0183B    39.25925926          .
100.  30nov2001      0183B   -20.21276596          .
------------------------------------------------
101.  31dec2001      0183B   -.6666666667          .
102.  31jan2002      0183B    9.395973154          .
103.  28feb2002      0183B              0          .
104.  31jan2000      0223B              0          .
105.  29feb2000      0223B    5.551515152          .
------------------------------------------------
106.  31mar2000      0223B    1.447178003          .
107.  30apr2000      0223B    .4279600571          .
108.  31may2000      0223B              0          .
109.  31jan2000      0226B              0          .
110.  29feb2000      0226B              0          .
------------------------------------------------
111.  31mar2000      0226B              0          .
112.  30apr2000      0226B              0          .
113.  31may2000      0226B            800          .
114.  30jun2000      0226B   -33.33333333          .
115.  31jul2000      0226B              0          .
------------------------------------------------
116.  31aug2000      0226B              0          .


This result is obtained from bysort firm year: egen SD=sd(return)

Thanks again.

IK

On Thu, Feb 27, 2014 at 10:47 AM, Nick Cox <njcoxstata@gmail.com> wrote:
> If you don't specify the year as a grouping variable, then values for
> different years are lumped together; that is precisely as it should
> be.
>
> Otherwise, I can't make sense of the claim that you get missing for SD
> with (e.g.) 6 non-missing values. -collapse- produces a missing SD if
> all values (or all but one) values are missing in a group, but not
> otherwise. (The "all but one" follows from the use of (n - 1) rather
> than n in the formula for SD, n being sample size as usual.)
>
> If you were expecting that missing values would be omitted from the
> -collapse- results, that expectation was incorrect.
>
> To make clear your perceived problem, we need to see data and output,
> e.g. for examples like that below.
>
> . clear
>
> . input firm year return
>
>           firm       year     return
>   1. 1 2000 0.875
>   2. 1 2000 1.2
>   3. 1 2000 0.9
>   4. 1 2000 0.35
>   5. 1 2000 0.98
>   6. 1 2000 1.4
>   7. 1 2000  .
>   8. 1 2000  .
>   9. 1 2000  .
>  10. 1 2000  .
>  11. 1 2000  .
>  12. 1 2000  .
>  13. 1 2001  .
>  14. 1 2001  .
>  15. end
>
> . collapse (sd) return, by(firm year)
>
> . list
>
>      +------------------------+
>      | firm   year     return |
>      |------------------------|
>   1. |    1   2000   .3560957 |
>   2. |    1   2001          . |
>      +------------------------+
>
> Nick
> njcoxstata@gmail.com
>
>
> On 27 February 2014 15:28, Ikechukwu M. <bigdoctor2004@gmail.com> wrote:
>> Thanks. Apologies for incorrect attribution to Nick Cox. What I meant
>> to say is that occurrence of missing values collapses to a missing,
>> even though I expected the missings to be ignored.
>> Thanks for the input - I have implemented what you both suggest and
>> the good news is that it resolves to the same thing so it is working
>> but not producing the desired output. I am ending up with missing
>> values even for firms that have 6 monthly observations for the year.
>>
>> The collapse code I used is this:
>> collapse (sd) sd_return=return, by(firm year)
>>
>> using bysort firm year: egen SD=sd(return)
>>
>> but when I omit the year, sd is appropriately computed but for all 10
>> years of the data, not partitioned into years.
>>
>> When I include the year, I end up with lots of missing observations.
>>
>> Thanks
>>
>> On Thu, Feb 27, 2014 at 4:21 AM, Nick Cox <njcoxstata@gmail.com> wrote:
>>> There are various "Nick"s around here. In my case, I wouldn't offer
>>> the explanation that the occurrence of missings will imply zero
>>> standard deviations with -collapse-, because it isn't true. More
>>> importantly, as you don't give the -collapse- code you used, we are
>>> reduced to speculation that somehow your -collapse- produced a
>>> collapse to constants, which have 0 SD.
>>> Nick
>>> njcoxstata@gmail.com
>>>
>>>
>>> On 27 February 2014 05:53, Ikechukwu M. <bigdoctor2004@gmail.com> wrote:
>>>> Thanks Kieran for your response. I tried that and it gives me all
>>>> zeros. I think it has to do with how stata treats missing values in
>>>> the collapse command. I had seen an earlier post by Nick regarding
>>>> this.
>>>>
>>>> I used bys firm : egen sd=sd(return) and I get values but they are not
>>>> partitioned by year. It gives me one SD for all the datapoints for the
>>>> firm.
>>>>
>>>> thanks
>>>>
>>>> On Wed, Feb 26, 2014 at 11:23 PM, Kieran McCaul
>>>> <kieran.mccaul@uwa.edu.au> wrote:
>>>>> ...
>>>>>
>>>>> Like this?
>>>>>
>>>>> clear *
>>>>>
>>>>> input firm str7 date return
>>>>> 1  "Jan2000"  0.875
>>>>> 1  "Feb2000"  1.2
>>>>> 1  "Mar2000"  0.9
>>>>> 1  "Jan2001"  0.35
>>>>> 1  "Feb2001"  0.98
>>>>> 2  "Jan2000"  1.4
>>>>> 2  "Feb2000"   .76
>>>>> 2  "Mar2000"  1.34
>>>>> end
>>>>>
>>>>> gen year = substr(date, 4,.)
>>>>>
>>>>> preserve
>>>>>
>>>>>    collapse (sd) sd_return=return, by(firm year)
>>>>>    tempfile ttt
>>>>>    save `ttt', replace
>>>>>
>>>>> restore
>>>>>
>>>>> merge m:1 firm year using `ttt'
>>>>> list
>>>>> bysort firm year: summ return
>
>>>>> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Ikechukwu M.
>>>>> Sent: Thursday, 27 February 2014 9:33 AM
>>>>> To: statalist@hsphsun2.harvard.edu
>>>>> Subject: st: generating annualized standard deviation of returns from monthly data.
>>>>>
>>>>> I am trying to compute standard deviation of returns for a panel data set and I am having a little difficulty.
>>>>>
>>>>> My data looks like this
>>>>>
>>>>> Firm    date                 return
>>>>> 1         Jan2000              0.875
>>>>> 1         Feb2000              1.2
>>>>> 1        Mar2000               0.9
>>>>> 1        Jan2001               0.35
>>>>> 1        Feb2001               0.98
>>>>> 2        Jan2000                1.4
>>>>> 2        Feb2000                .76
>>>>> 2        Mar2000                1.34
>>>>>
>>>>>
>>>>> I would like to compute the annualized standard deviation of returns for each firm and return one number for each firm in each year.
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