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Re: st: Identifying Experiment subjects that belong in both the Placebo and Experiment Groups


From   Beatrice Benavidez <beatricestata1711@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Identifying Experiment subjects that belong in both the Placebo and Experiment Groups
Date   Mon, 22 Oct 2012 14:30:20 +0400

Thank you for your reply. But what if my dataset is structured like below:

Date          ID          Received
18/1           3            Treatment
19/1           3            Placebo
20/1           3            Treatment
18/1           4            Placebo
18/1           4            Treatment
18/1           4            Placebo
18/1           4            Treatment

The particular ID's first and last observation may be the same but the
in-betweens are different.

The line "bysort ID (Received) : gen bad = Received[1] !=
Received[_N]" may not work as [1] and [_N] only deals with first and
last respectively.

How would I run this where the number of date/treatment occurrences
differs from one ID to another? How do I take into account if the
Received observation is different from one occurrence to the next and
not just from the first and last occurrence.

Thank you.

Kind regards,


Beatrice
------------------------------
Date: Sun, 21 Oct 2012 12:44:33 +0100
From: Nick Cox <njcoxstata@gmail.com>
Subject: Re: st: Identifying Experiment subjects that belong in both
the Placebo and Experiment Groups

This is an FAQ. See

How do I list observations in a group that differ on a variable?
http://www.stata.com/support/faqs/data-management/listing-observations-in-group/

bysort ID (Received) : gen bad = Received[1] != Received[_N]

Nick

On Sun, Oct 21, 2012 at 12:38 PM, Beatrice Benavidez
<beatricestata1711@gmail.com> wrote:

> I have a dataset like below but for thousands of subjects (IDs).
>
> However, in my experiment a particular subject may have received both
> the treatment and placebo at the same or different dates (such as
> person of ID 2 and ID 1 respectively). This occurrence would then
> invalidate the experiment. I would then like to find a way to identify
> and flag those subjects.
>
> Date          ID          Received
> 1/1             1           Treatment
> 1/1             2           Treatment
> 1/1             2            Placebo
> 17/1           1            Placebo
> 18/1           3            Treatment
>
> I know I'd have to do bysort ID: gen flag = 1 if ...
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