st: Indexing Question

["kelly johnson" <econometrics@hotmail.com>]

Hi,

I have a question regading calculations and indexing. Below I have an except 
of a larrge data set. How can I calculate the percentage change in the 
variable X from the earliest date to the last date (e.g. in the case where 
id==1, the percentage change in X from 7/1/05-7/6/05). I want to do this by 
id for all my observations (i have thousands of obsevations and the date 
periods are of varying lengths...). I know it's of the 'by id:' type of 
statements, but I just can't get it right. Thank you.

Kelly


       date   id       X
    7/1/05    1      .2
    7/2/05    1      .3
    7/3/05    1      .2
    7/4/05    1      .1
    7/5/05    1      .5
    7/6/05    1      .6
   6/16/05    2      .4
   6/17/05    2      .4
   6/18/05    2      .4
   6/19/05    2      .2
   6/20/05    2      .1
   6/21/05    2      .3
   6/22/05    2      .5
   4/11/05    3      .2
   4/12/05    3      .8
   4/13/05    3      .7
   4/14/05    3      .8
   4/15/05    3      .2
   4/16/05    3      .2
   4/17/05    3      .3
   4/18/05    3      .1
   4/16/05    3      .5
...

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