The Dow Jones report is compiled of data sent from many different 
counterparties. The lovely people at Dow Jones painstakingly analyze the data 
to ensure its accuracy. Averaged together, these prices become the Dow Jones 
daily index price. And that's the long and short of it. 

The process, as you've guessed by now, is a little more complicated than 
that. For one thing, Dow Jones looks at each counterparty's sales to reach an 
average of all the prices. It would be redundant for each counterparty to 
ALSO report their purchases from each other. Therefore, when calculating the 
Dow Jones data, we only include purchases from counterparties who ARE NOT 
participants in the Dow Jones survey. Following is a simple example:

Participant List  NP-15 Purchases  NP-15 Sales  Reported NP-15 Purchases 
Reported NP-15 Sales
Sempra  Sempra - $250   Sempra - $250  Avista - $270   Sempra - $250
Duke   Duke - $260   Duke - $260      Duke - $260
Enron   Avista - $270   Avista - $270      Avista - $270

Now that's simple!

Following is the participant list for Dow Jones' survey of trading at NP-15 
and SP-15 delivery points. Deals with these counterparty names need to be 
excluded from the calculation of PURCHASES at NP-15 and SP-15 delivery points.

American Electric Power - Amerelecpo
Avista Energy - Avistaene
Duke Energy Trading and Marketing - Dukeenetra
El Paso Merchant Energy
Enron Power Marketing, Inc. - EPMI
Idaho Power Company - Idacorpene
PacifiCorp - PACE
Pacific Gas & Electric Company - PG&E
Powerex Corp. - PWX
Puget Sound Energy, Inc. - PSPL
Mirant Americas Energy Marketing (formerly Southern Company Energy Marketing) 
- SCEM
TransAlta Energy Marketing (US) Inc. - Transalt

So I've probably succeeded in confusing you even more, but please feel free 
to come bug me with questions. Good luck!

Kate