General Discussion

The Problem With Online Sales Sites as Sales Indicators:

* Online sales are just a fraction of overall sales: about 20% of overall book sales in 2007 [source]
* Overall sales at a given site can be as much as $4 billion (amazon) or as little as $26 million (books-a-million) -- and that $4 billion number at Amazon is the sales of 'media' -- they don't differentiate on their corporate reports between books, CDs, DVDs, and downloads.  [here's that 2007 AR as a pdf; the breakdown of sales by type and region is on pg. 34] -- oh, and a number of sites are privately owned (or so small that they don't have to file annual reports) (or both) so any details of their sales, past what they may deign to share with us, are an abssolute mystery.
* the fraction of manga sales online can vary quite a bit as a percentage, from site to site, from publisher to publisher, and even from title to title -- since we don't know what the actual numbers are we can't know for sure, but I'll posit that Yaoi is selling much better online than in stores.
* 'bestseller' rankings will be different for different sites not just because of raw sales, but also because a bestseller computation may include historical data (a year of sales gives different results from a week of sales)
* the ranking of manga depends in largest part on what a site calls "manga".  For example, In Odd We Trust, the OEL Manga from Del Rey, Dean Koontz, and Queenie Chan is a high ranking manga on many sites, but not at Barnes & Noble -- because bn.com doesn't think it's a manga title.

Additional Problems with Amazon:

* Amazon doesn't use hard-and-fast categories or even 'tags' as bloggers understand them, they have an odd system where any given title can be considered part of (and simultaneously ranked in) many different categories and sub-categories
* A category listing on Amazon also depends on past searches and customer feedback.  My favourite example is Chris Hart.  He wrote a few "Manga Mania" how-to books -- and because of those any book that comes up on a search for 'Chris Hart' is included in their Manga Listings.  There is even an Organic Chemistry text that is ranked "#2 in Books > Comics & Graphic Novels > Manga > By Creator > Hart, Christopher" over on amazon even though Chris Hart didn't write it; among the co-authors are David J. Hart & Christopher M. Hadad
* I think you have already noted the inconsistencies in the anime listings; quite a few plain animation titles with absolutely no link to Japan or to American anime licensees show up in the anime category.
* Hourly Bestseller Lists are exactly that:  sales from the past hour.  If I had the money and the urge, I could probably place Blood Alone vol 4 in the top 100 just by buying 20 copies -- except no one would know, because in an hour and a half a new chart would be in place.

Ways around these limitations:

* Amazon also has a manga category listing which is different from their hourly bestseller charts: Link.  This list can be sorted by 'bestselling', 'publication date', or 'average customer review' depending on how you want it.  It still has the same errors on it, but will represent sales over a longer time period than just an hour.
* One can check the hourly bestsellers multiple times a week (or even in just a day) to get an average

Or,

You know,

One could check Amazon's Manga Category weekly, and their hourly bestsellers 4 times a week, and also check eight other online sales sites (B&N, Borders, Books-a-Million, Buy.com, DeepDiscount.com, Powell's, Tower, and Chapters of Canada)  (and some of those multiple times a week too) and then come up with some sort of weighted scale to assign points to titles based on how they rank on all these sales sites at the time checked, and then one could set up a spreadsheet to calculate not only the top manga volumes, but (depending on how detailed one makes the individual book listings in this hypothetical database & how many data points one chooses to track) it might also be possible to generate charts based on series, not just individual volumes -- or on publisher, or publication date.

You'd have to be a Big Honkin' Nerd and A Little Nuts besides, but it can be done.

The only drawback is that all the work is invisible to the masses; if they see a chart on your blog they assume you're just copying from some other 'official' news site.  No one has any idea that the data and analysis are original work, even if you post commentaries and FAQs and long explanations of the methodolgies, or huge quarterly and annual charts.  You can waste upwards of 20 hours a week and get no love from the internets.

Oh, I know I can't match USA Today and their numbers -- I mean, I only manage to beat them by two or three days most weeks.  And all I post are manga titles.

For the week ending 11 January (the same time period from the most recent USA Today chart) the top 10 manga volumes according to estimates based on online sales rankings were

1. ↑2 (3) : Naruto 33 – Viz Shonen Jump, Dec 2008 [720] ::
2. ↔0 (2) : Naruto 32 – Viz Shonen Jump, Nov 2008 [700.2] ::
3. ↓-2 (1) : Naruto 31 – Viz Shonen Jump, Sep 2008 [674.1] ::
4. ↑1 (5) : Fruits Basket 21 – Tokyopop, Nov 2008 [653.9] ::
5. ↑1 (6) : Vampire Knight 5 – Viz Shojo Beat, Sep 2008 [646.7] ::
6. ↑1 (7) : Bleach 24 – Viz Shonen Jump, Sep 2008 [621.3] ::
7. ↓-3 (4) : Bleach 25 – Viz Shonen Jump, Dec 2008 [620.5] ::
8. ↔0 (8) : Naruto 30 – Viz Shonen Jump, Jul 2008 [616] ::
9. ↑1 (10) : Vampire Knight 1 – Viz Shojo Beat, Jan 2007 [611.1] ::
10. ↓-1 (9) : Bleach Souls: Official Character Book – Viz Shonen Jump, Oct 2008 [608.5] ::

The Top 10 series (using a formula that considers the score of the top 2 ranking volumes of a given series, plus one-tenth of the scores of all other ranking volumes) were

1. ↔0 (1) : Naruto – Viz Shonen Jump, Jul 2003 [3011.27] ::
2. ↔0 (2) : Bleach – Viz Shonen Jump, Jun 2004 [2062.26] ::
3. ↔0 (3) : Fruits Basket – Tokyopop, Feb 2004 [1856.87] ::
4. ↔0 (4) : Death Note – Viz Shonen Jump Advanced, Oct 2005 [1723.46] ::
5. ↔0 (5) : Vampire Knight – Viz Shojo Beat, Jan 2007 [1460.7] ::
6. ↔0 (6) : Fullmetal Alchemist – Viz, Apr 2005 [1162.54] ::
7. ↑1 (8) : Rosario+Vampire – Viz Shonen Jump Advanced, Jun 2008 [1094.08] ::
8. ↓-1 (7) : Kingdom Hearts – Tokyopop, Oct 2005 [1023.87] ::
9. ↔0 (9) : Warriors – HC/Tokyopop, Apr 2007 [934.42] ::
10. ↑1 (11) : Chibi Vampire – Tokyopop, Apr 2006 [904.77] ::

[more posted at www.rocketbomber.com/category/rankings]

I've only been doing this on-and-off for the past 18 months.  (66 of the past 80 weeks -- hey, I'm only human.)  If you had questions about online sales, Gia, you could have just asked.  ;P 
 
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I know I probably sounded a bit snarky or even bitchy --  My sense of humor can be a tad dry and I overuse sarcasm.   I assure it, it was all in good fun and intended in the spirit of collegial co-operation, sharing what I've figured out about online manga sales listings and their limitations.  My humblest apologies if you felt I was unfairly judging and  'correcting' your work. 
-- The shameless self-promotion, though, that was intentional and I stand by every link.  :)

Oh, and here's the link to the Anime Category at Amazon if you wanted to reference that instead of the hourly bestsellers next Monday:  Link