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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 13:24:43 -0500

Thank you! That did it.
I appreciate all the help.
IK

On Thu, Feb 27, 2014 at 12:13 PM, Nick Cox <njcoxstata@gmail.com> wrote:
> You are using the name -year- but that name is wildly misleading here.
>
> The values of year are, it seems, individual daily dates.
>
> The key point of -collapse, by(firm year)- is how many observations
> there are for each _distinct_ combination of -firm- and -year-. For
> your sample data shown here all the groups are represented by _single_
> observations, with the result explained earlier, the SD is returned as
> missing (because sample size - 1 is 0).
>
> You have to produce a true "year" variable for what you want to work,
> e.g. by using -yofd()-.
>
> Nick
> njcoxstata@gmail.com
>
>
> On 27 February 2014 16:56, Ikechukwu M. <bigdoctor2004@gmail.com> wrote:
>> 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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