st: Selecting observations

[Jacob-Jan Koopmans <jacob-jan.koopmans@student.uva.nl>]

Dear Statalist,

I have a problem with selecting observations.

I would like to compare the health characteristics of people that drop
out of insurance with that of people that remain insured.

In my data-set I have 4 years and want to know whether people that
drop out of insurance between year 3 and 4 but were insured in the
first 3 years are more or less healthy compared to the individuals
that remain insured in year 4. For this I would thus like to drop
observations that were uninsured in year 1 to 3 and in year 4 I would
like to keep the individuals that became uninsured.

Dropping out the observations that were uninsured in the first 3 years
is simple.
Initially I started with simple drop commands
drop if has_health_insuranceA==1 if year==1
drop if has_health_insuranceA==1 if year==2
drop if has_health_insuranceA==1 if year==3

However, in year 4 I now want to select individuals which were insured
in year 1, 2 and 3 but not anymore in year 4. And have no idea how to
do this.
Is there anyone who could help me with this?

Kind regards,
Jacob-Jan Koopmans
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