This post was inspired by “ aNobii Library and copies sold“ (in Italian), by jumpinshark. I do also enjoy scraping various sites, aNobii included before they hired me:), and I think that looking from the outside one often has ideas that would otherwise struggle to emerge from the inside. The idea that not all books have the same ratio sales / presence-in-aNobii-libraries is indeed interesting: some books are extremely successful on aNobii but don’t sell much, others the other way around. So I could not resist using some probability distributions and see if I could generalise the results obtained by jumpinshark. Note that I did not use any internal aNobii data for this.
Unique aNobii visitors in Italy
Before starting, however, I must underline that there was no drop in the number of unique visitors we had (contrary to what DoubleClick estimates, as reported by jumpinshark). Even in Italy, we never dropped below 30.000 unique visits per day and we are still (very well!) above 70,000 per month. Above you can find the graph taken from Google Analytics, without numbers, which shows unique visitors per month in Italy during the past twelve months: it’s constant.
That said, let’s go back to jumpinshark. As mentioned, his analysis is correct, and may be further formalized, using distributions instead of averages.
The analysis –a little more formal
You can find on this Google Spreadsheet all results. Let’s list the assumptions:
- The distribution of numbers of books purchased per year is a Pareto-Zipf with exponent 2: If I have 100 people in Italy who have bought 1 book, I’ll have 100 / 2 ^ 2 which have bought 2, 100 / 3 ^ 2 which I have bought 3 etc. See Column B of the spreadsheet. (With this distribution, strong readers who read 10 books a year are more than ~ 2 million).
- It is n times more likely that a person with n books joins aNobii than a person with 1 book. See column C.
- Each book has its “resonant reader.” For example, I assume that the “resonant” readers for Umberto Eco buy 15 books a year (kind of intellectual), readers of Benedetta Parodi (TV show lady) read just 1 book per year . I say “resonant” because usually in these cases one uses the Cauchy distribution, which is used in physics precisely for resonances. Resonant does not mean exclusive: other readers might like Eco and Parodi, only a bit less. See column D & E and cell G9, H9.
End of assumptions. The distributions above are quite standard in these cases, and show that when an author resonates with avid readers, like Eco does, s/he has a better chance of appearing on aNobii than a more pop book with same amount of sales. This stems from the fact that a voracious reader is more likely to end up on aNobii, although there are many members of aNobii with very few books in the library, just as in the hypothesized distribution.
So for every aNobii-user who owns Eco, there are about 230 people on the street that have actually bought it. For Ms Parodi the ratio is 1 to 1000 instead. Still, as noted by jumpinshark, there are other factors: I bet that “ aNobii, the reading worm“, a book composed by aNobii reviews, has a ratio close to 1:) Anyway, even if the numbers are far from perfect, the result is not bad, IMHO….
