Can you expand on that? The topic is really interesting
thanks.
Basically retailers would like to know total market sales data, right? Makes assortment and purchasing decisions easier. They also want a view if they're under or over buying or missing out.
Problem is they only have their own sales data, the total market data is spread across all the other retailers and many of them are probably competitors.
So Nielsen and NPD essentially act as data brokers. They purchase and collate data (often cleansing it so far as I know although I'm less familiar with NPD) then re-sell it to retailers and other groups for whom it has value to know the total market picture (or close to it 'cause yes NPD doesn't cover everything).
For example I was in a meeting with a large UK retailer talking to their electronics buying director and he buys UK data for games, etc for exact same reason: he wants to know how say Watch Dogs sold in total vs how much his department bought and sold and evaluate if they bought well or not for future reference.
Central to this is all the retailers are selling the same thing in this case.
No think about films. If I'm Fox would I really buy data on how Warner's films performed? Does it have much value when the film Fox is making is different, has a different script and different actors?
Sure a little but not very much. Hence in the film industry nobody is trying to make money as a broker for that information and hence it tends to be available without cost and unhidden.
Technically you could argue Fox and Warner don't have to share (haven't looked into that specifically) but the medium has a history aligned with music for charts and allowing public to know what's most popular, etc.
So with games you have the data hidden as it has a value so long as it isn't freely and openly available (hence why Aqua and others were rightly twitchy about people on GAF being too gung ho about re-posting and collating leaked info) whereas the low or zero value data on film performance is freely available via Boxofficemojo and others.
That's the basics as I understand it anyway.