st: Laspeyres index

[Tomáš Houška <xbender@gmail.com>]

Dear Statlist,

I would like to ask you for a help with computing Laspeyres index.
This price index is defined as Sum(Pn*Q0)/Sum(P0*Q0), where Q0 and P0
and prices in the first period and Pn is the price in the current
period.

I have panel data (available for download here:
http://is.muni.cz/www/99107/test_file2.dta    (size 84k)) where I have
"item_code" (identifier of the product), "store" (panel variable),
"week" (time variable), "move" (sold quantity), "price" and "size_cat"
(category identifier).

I would like to calculate Laspeyres index for each category over time,
but I cannot get the multiplication by the first period right. I am
looking for some clean solution, because I in my whole dataset (much
bigger than test_file available for download) are approx 150 types of
products, 30 stores and 300 weeks.

Would you please give me an advise on how to calculate the Laspeyres
index? Help will be very appretiated.

Thank you

Tomas
Masaryk University
*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/