iTunes Sales Not 'Collapsing' After All

john82 writes "Earlier this month we had a report from Forrester, based on a random sampling of 2,000 credit card accounts, that purported to show that iTunes sales were crashing. Now comes another survey from Reston, VA-based ComScore which indicates the exact opposite. ComScore's report which is based on actual iTunes sales shows a 84% increase during the first nine months of this year compared to the same period last year. Meanwhile the author of the Forrester report, Josh Bernoff, noted in his blog yesterday that they shouldn't be pummeled just because everyone took what he wrote and ran with it."

Comments

Re:Own up to your reporting

[dcollins]

"Seriously though, did you *really* think that a sample size of just over 1000 purchases on credit cards obtained through a back channel source is a reliable sample size for the number of iTunes purchases?... Thats just high school statistics by the way..."

I'm a college professor of statistics. I don't think you can actually quote a high school statistics book which says that sample size is too small. In general, a sample size of 1,000 gives 95% confidence that your result is within +/-3% of the actual result. This is *regardless* of population size - that's how statisatics work, due to the Central Limit Theorem.

http://en.wikipedia.org/wiki/Sample_size
http://en.wikipedia.org/wiki/Central_limit_theorem

Now, the first thing that pops into my head is why only credit-card purchases? And even more fundamentally, why would the same people need to buy music, after they just went on a music-buying spree? I would think the opposite. That was the thing that made me skeptical of the report yesterday in the first place.