Ebooks are gaining share. I expected more of a 'September bump' due to the introduction of the Kindle 3. The lack of a large bump doesn't mean much, September is a month that in the start of the end of the year ramp up in ebook sales. In many ways the October data will be far more interesting.
To the charts (with further comments):
I'm plotting the data in two forms.
1. A plot chronological with time to show the long term trend
2. By month, with each year being its own line. This shows seasonal trends which are strong in book sales.
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The 2nd graph really shows the growth of ebook sales year over year. It also shows:
1. Device sales drive ebook sales
2. The beginning of the year 'tiff' hurt ebook sales
3. Ebook sales are back on a growth trend
4. Kindle 3 sales have yet to impact ebook sales
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As ebook sales have increases, we see that mass market paper back sales have mostly drifted in their normal band.
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When plotted by year, we see mmpb sales are weak, but there is no trend with ebook sales. If anything, I would say over-pricing or a poor 'product mix' is more to blame than ebooks.
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Paperbacks sold poorly in September. In the past, September was one of the strongest months for paperback sales (if not the strongest). This year's weak showing is probably due to the customer switch to ebooks.
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The year to year comparison clearly shows a missing peak. Who didn't order paperbacks? Some retailer (or several) didn't stock up this year on adult paperback pbooks... This could be corrected in October, so it will be worth looking at the next data set.
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Harcover sales are in their normal band:
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Year on year comparisons show that 2009 had an abnormally strong September. 2010 hardcover sales are on the weak side, but that is probably just the economy.
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Conclusion:
Ebook sales are strong and have a very seasonal tendency for growth (end of year and post-Christmas). It looks like adult paperbacks are taking a hit with increased ebook sales. Otherwise, it does not look as if ebook sales are impacting print sales. Ebook sales growth is also greater than the impact to paperbacks, so it is possibly ebooks are growing the market!