st: Counting firms in a panel dataset

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

Hi, Statlisters. I am using -codebook- to count the number of agents in a
panel dataset under different criteria. Under a criterion I get 408 agents
and under another one I get 397. I have an intuition about the cause of this
difference and I would like to check it out, but I do not know how to do it.
To help make clear my point, (the relevant part of) my dataset looks similar
to this,

id     startdate    date   var1      var2       mean_var1
1           189          187     10           .               10.75
1           189          188     11           .               10.75
1           189          189     11           1              10.75
1           189          190     11           .               10.75
2           192          189     10           .               10.5
2           192          190     10           .               10.5
2           192          191     11           .               10.5
2           192          193     11           .               10.5

Using the command -codebook id if mean_var1 != 11- I get 408 agents, but
using the command -codebook id if mean_var1 != 11 & (var1 == 10/var2 | var1
== 11/var2)- I get 397 agents. My intuition is that this happens because
there are agents (like agent 2) that do not have the observation
corresponding to the startdate. If I am right adding this requirement to the
command -codebook id if mean_var1 != 11- should count 11 agents, but I do
not know how to include that requirement. Will anyone please help with this?
Thanks in advance.

Miguel.

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