Re: st: Observations that keep a feature... an additional problem

["Miguel Angel Duran Munoz" <maduran@uma.es>]

Nick, after reducing the sample using your suggestion, I have checked the
number of agents that there are per period. And the number is increasing
in time. I guess this is due to the fact that agents joining the sample as
time goes by and satisfying the requirement of being above the threshold
are not excluded. Is there any trick to avoid including them? Thanks
again.

> 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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