E-books lost a little bit of sales ground in the third quarter of 2014, according to data from the latest survey of book-buying behavior from Nielsen Books & Consumers. E-books accounted for 21% of unit sales for the year to date through September 30, down from 23% in the January-through-June period. After the first six months of the year, paperbacks represented 42% of units sold; after a slight increase in sales during the third quarter, their share rose to 43%. The hardcover segment’s share of purchases held even at 25%.

The mystery and romance categories had the largest shares of e-book units, at 32% and 36%, respectively, but in both genres paperbacks still accounted for the highest percentage of units sold. In mystery, paperbacks accounted for 37% of purchases; the paperback format took 52% of romance purchases. The Nielsen data also show that e-books lost some of the ground they gained in the young adult category in the first half of 2014, when e-books were 30% of unit sales (on the strength of hot sellers, such as the Divergent series, that performed well in the e-book format). By the end of the third quarter, however, e-books were down to 27% of units sold in the young adult segment.

Despite the slight decline in e-books’ share of units in the third quarter, where consumers bought books in the period shifted very little. E-commerce outlets, led by Amazon, accounted for 39% of unit purchases at the end of the first six months of 2014, which remained the same through September. Bookstore chains, too, had the same share at the end of both the six-month and nine-month periods, at 21%. The two categories where e-books have the highest sales—mystery and romance—also did best at e-commerce outlets, with online retailers accounting for 44% of mystery unit sales and 47% of romance purchases through September. Among the major book categories, the children’s segment (excluding young adult), was the least popular category with e-commerce outlets, accounting for 26% of units in that channel.

The Nielsen survey of consumers also found that 57% reported buying their e-books through Amazon in the first nine months of 2014. Amazon’s single closest competitor was BN.com/Nook, which had a 14% share of unit e-book purchases through the first nine months of the year. Apple had only a 6% share. The “other” category had a 20% share, and it is possible some consumers did not realize which e-bookstore they were using to download certain e-books.

Though Amazon also had the largest share of devices that consumers reported using to download e-books, its lead over Apple was much less substantial than the gap between Amazon and Apple in e-book sales. According to Nielsen, 23% of consumers used a Kindle to download e-books in the first nine months of 2014, and another 21% used the Kindle Fire. Apple’s iPad was used by 18% of consumers to download e-books, while 4% used an iPhone. Barnes & Noble’s Nook had a 9% share of e-book downloads.

The 2014 edition of the Nielsen Books & Consumers survey focuses on sales of new books (frontlist and backlist), but unlike past surveys excludes used book sales—a switch that makes it difficult to compare results in prior years.