Internet Retailer Pricing Data
We compiled a sample of 2207 books from various
sources.7 From June 2001 to August 2002, we collected
daily price data on these books from all the bookstores
returned by a search on mySimon. Eliminating duplicates
and books not carried by any of the mySimon bookstores
left 1640 books. We prefer that price changes in the data
reflect the mixed-strategy discounting of retailers rather
than systematic changes from price shocks (e.g., net price
changes due to a switch over to free shipping) or reservation
price changes. Price data collected over longer periods have
a greater risk of being contaminated by systematic price
adjustments. To alleviate this problem, our empirical analyses
use daily pricing data on the 1640 books for a period of
26 days in June 2002. This month represents the most
recent period for which we have complete data from all the
retailers and no systematic price adjustments. This 26-day
window also spans a relatively short period to minimize
reservation price adjustments.