Figure 118 Oct 2026From “What is freemium?”

Paperback copies per title before and during the experiment, by arm

Paperback sales fell in all three arms. They fell by about a third in the control titles and by less than a tenth where a hardcover or an e-book had been added.

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Figure 1Paperback copies per title before and during the experiment, by arm

Source: Gu et al. (2018), p. 17, Table 3: mean paperback quantity per title in the 32 weeks before and the 32 weeks during the experiment; 668 titles with an added hardcover version, 667 with an added e-book version and 716 control titles, randomly assigned within blocks of paperback price and popularity. The free PDF stayed free in every arm.

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A GKM18-C4 Difference-in-differences with a negative binomial model: Treat × Post positive and significant (hardcover 1.207, p < .05; e-book 1.795, p < .01); the authors translate the marginal effects at means into 1.2 and 2.6 more paperback copies per title (772 and 1,722 copies), printed without significance marks and with standard errors .931 and 2.262 (Table 4, p. 19); without two blockbuster titles, one per treatment arm, .5 and .4 copies per title (p. 20); Table 3 raw mean paperback quantity per title, before and during: hardcover 1.58 and 1.43, e-book 2.93 and 2.79, control 0.86 and .57; the arms did not differ significantly at .05 before the experiment by one-way analysis of variance (pp. 17 to 20): "by 1.2 copies per title, which can be translated into an"; "of the paperback version increased by 2.6 copies per title"; "version can increase sales of the paperback version by .5 copies"; "paperback version by .4 copies per title, which can be translated"; "one title under the hardcover condition and one title"; "Paperback quantity 1.77 1.58 2.93 0.86"; "Paperback quantity 1.57 1.43 2.79 .57"Gu, Kannan & Ma (2018) · Gu, Kannan & Ma. (2018)

Grades: A, verified against the printed page of the primary source · B, primary source, text layer only · C, authoritative secondary · D, reported.

From the essay

Pricing & revenue architecture

What is freemium?

Freemium is a pricing choice: a basic version at a price of zero beside one or more paid ones. Studies of books, web content and apps show the trade-offs.

18 Oct 2026

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Isoglu, S. (2026). Paperback copies per title before and during the experiment, by arm [Figure]. isoglu.com. https://isoglu.com/insights/exhibits/isoglu-2026-what-is-freemium-fig01/

BibTeX

@misc{isoglu-2026-what-is-freemium-fig01,
  author = {Isoglu, Sinan},
  title = {{Paperback copies per title before and during the experiment, by arm}},
  year = {2026},
  howpublished = {Figure 1, isoglu.com},
  url = {https://isoglu.com/insights/exhibits/isoglu-2026-what-is-freemium-fig01/},
  note = {From the essay {What is freemium?}}
}

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  <a href="https://isoglu.com/insights/exhibits/isoglu-2026-what-is-freemium-fig01/">
    <img src="https://isoglu.com/social/isoglu-2026-what-is-freemium-fig01.png" alt="Figure 1: Paperback copies per title before and during the experiment, by arm" width="3200" height="2400">
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  <figcaption>Figure 1: Paperback copies per title before and during the experiment, by arm. Source: Gu et al. (2018), p. 17, Table 3: mean paperback quantity per title in the 32 weeks before and the 32 weeks during the experiment; 668 titles with an added hardcover version, 667 with an added e-book version and 716 control titles, randomly assigned within blocks of paperback price and popularity. The free PDF stayed free in every arm. <a href="https://isoglu.com/insights/exhibits/isoglu-2026-what-is-freemium-fig01/">View exhibit</a>.</figcaption>
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