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Re: st: Observations that keep a feature in the whole sample period


From   "Miguel Angel Duran Munoz" <maduran@uma.es>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Observations that keep a feature in the whole sample period
Date   Wed, 22 May 2013 18:49:46 +0200 (CEST)

Thanks, Nick. I have finally been able to go through your proposal.

> Assuming variable names
>
> agent  period  score
>
> it seems that you want something like
>
> bysort agent (period) : gen first3 = _n < 4
>
> egen max_first3 = max(score / first3), by(agent)
>
> egen min_rest = min(score / !first3), by(agent)
>
> keep if max_first3 > 0.9 & min_rest > 0.9
>
> For the division trick in the -egen- call see e.g.
>
> http://www.stata.com/statalist/archive/2013-03/msg00917.html
>
> (reference included therein).
>
> Nick
> njcoxstata@gmail.com
>
>
> On 22 May 2013 15:03, Miguel Angel Duran Munoz <maduran@uma.es> wrote:
>> Nick, thanks for your help. I hope you can help me with another doubt.
>> For
>> a similar analysis to that of my first message, assume I want to keep
>> those agents that that have overpass the threshold before a certain
>> period
>> and then have been over it in the rest of the sample period.
>>
>> To illustrate the idea, consider the following (data refer to
>> consecutive
>> periods and the threshold is, eg, 0.9):
>>
>> Agent 1: 1    1    1    1    1...
>> Agent 2: 0.8  1    1    1    1...
>> Agent 3: 0.8  0.8  0.8  1    1...
>> Agent 4: 0.8  0.8  0.8  0.8  1...
>>
>> I want to keep the first three agents because they have overpassed the
>> threshold before period 4 and then have been over the threshold in the
>> rest of the sample period, but I do not want to keep agent 4.
>>
>> Thanks in advance.
>>
>> Miguel.
>>
>>
>>
>>> Correct on -keep-. Sorry about that.
>>>
>>> The -sort- order
>>>
>>> bysort entity (const_a) :
>>>
>>> ensures that -const_a[1]- is the lowest for each agent, not the first.
>>> If the lowest value for each agent is above the threshold, then all
>>> the observations for that agent  are above.
>>> Nick
>>> njcoxstata@gmail.com
>>>
>>>
>>> On 21 May 2013 23:16, Miguel Angel Duran Munoz <maduran@uma.es> wrote:
>>>> Thanks, Nick. I guess you mean -keep- instead of -drop-. Nevertheless,
>>>> the
>>>> command that you suggest would not guarantee that I keep the agents
>>>> that
>>>> have been above the threhsold for the whole sample period (ie, I would
>>>> be
>>>> including agents that were above the threshold in the first period and
>>>> then might have been above or below it).
>>>>
>>>>> Sounds like
>>>>>
>>>>> bysort entity (const_a) : drop if const_a[1] > 0.09716
>>>>>
>>>>> Nick
>>>>> njcoxstata@gmail.com
>>>>>
>>>>> On 21 May 2013 23:01, Miguel Angel Duran Munoz <maduran@uma.es>
>>>>> wrote:
>>>>>> Hi, Statalisters. I want to focus on agents in my dataset that have
>>>>>> a
>>>>>> particular feature; specifically, for those agents, and for each and
>>>>>> every
>>>>>> period (out of 64), the value of a variable (const_a) is larger than
>>>>>> a
>>>>>> particular threshold (0.097116). I have done what I show below.
>>>>>> Nevertheless, I have realized that some of my agents are not in the
>>>>>> sample
>>>>>> since the first period, so what I am doing would mistakenly
>>>>>> eliminate
>>>>>> them. Will anyone help to solve this problem? Thanks in advance.
>>>>>>
>>>>>> bysort entity (date2): gen obs=_n
>>>>>> drop if const_a<0.097116
>>>>>> by entity: drop if obs[_N]<64
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