One thing I can’t say enough is that data should be interpreted with a healthy amount of caution and second-guessing. This is especially true for manga charts, when a combination of ridiculously high weekly thresholds and the desire to have fast data on the effects of currently-airing anime can lead to some very incomplete and erroneous interpretations of the facts.
I’ve already done a few case studies on how Oricon and publisher claims can differ for series where the publisher boasted of some particular print total (usually in an insert on a volume of the series or a magazine). Those cases are enlightening, but not necessarily general, since there’s a heavy element of volunteer bias involved in which series get their totals reported. Recently, though, I found a fairly large list of distributor claims of print volume totals (via Shuppan Shiyou, see post #99 here), which contains latest-volume printing data for over 100 series published in 2013. It still isn’t totally general, but is at least a tad more representative of manga at large. In order to get a better idea of how much Oricon underestimates the “average” series, I took the weekly-charts total for a volume and compared it with the given print total for the same volume. The results of this comparison (which can be found here) highlight some large and inconsistent discrepancies between the Oricon figures and the official publisher totals.
Notes on the data:
-The post states that the data only goes until September 2013, but the given data includes second-printing info on volumes released after that, so I assume it goes until the end of the year.
-If a volume never charted, I assumed it was close to the threshold that week and assigned it a correction factor of 20% (i.e. assuming Oricon would have gotten about 20% of the print total if the thresholds had been lower). This is probably being generous.
-The initial sample contained 108 total series. I excluded Shirokuma Cafe, Tonketsu, and Kakukaku Shikajika due to inconsistencies in the volume numbering and/or lack of available data. The final sample contained 105 series.
-Ao Haru Ride and Skip Beat both put up Oricon totals in excess of their respective publisher print claims, which is a little weird.
First up, there are a substantial number of volumes which got 100,000+ print runs but never made the Oricon charts. Some of those are long-runners (Golgo 13, Shizuka Naru Don, Oishinbo) with presumably older, more casual fans. There was one series though, which was only 8 volumes long at the time: Obata Fumio’s Shimauma. This series only ever charted once, when its fifth volume made the charts with less than 15,000 copies in its first week, but has a print total in excess of 1 million copies. That’s damn near Yuruyuri territory, and it didn’t even have an anime adaptation to explain away the long tail. All in all, 15 volumes in the sample never made the Oricon charts.
Speaking of long-runners with potentially more casual fans, it’s interesting to note that Hajime no Ippo v105 (380,000 copies) got a larger print run than both Ahiru no Sora v38 (370,000 copies) and Ace of the Diamond v39 (340,000 copies), even though the latter two both beat it on the Oricon charts by 100k copies. Similarly, Mix v3 got more copies (660,000) than Magi v19 (640,000), despite the latter out-Oriconing the former by nearly 200k. Vagabond (900,000 copies) only sold 43% of its print run above the Oricon thresholds, seemingly underperforming a whole lot of series it was downright outclassing.
On average, the Oricon weekly chart total of a volume seemed to correspond to about 61% of its print total. But the spread of that underestimation is ±23%, which is pretty huge. This happens for a number of reasons. A series might have a really long tail, or take off on its second or third volume and end up getting a lot of reprintings that take time to fully sell. There *are* some general patterns in the data: the least-underestimated seem to be series with a larger percentage of female fans, long-runners tend to be underestimated because their fans are more casual and don’t buy right away, and series with bigger print runs (and thus longer on-chart tails) tend to be less underestimated.
The real issue here is that there’s no consistent way to predict which series will be severely versus slightly underestimated. There exist outliers and counterexamples for each of the above trends: Kuragehime is a female-oriented work that’s underestimated beyond the sample average, Kingdom is a 30+ volume series which is very slightly underestimated, and Vagabond is heavily underestimated despite a 900k print run.
Many of these deviations seem to be explicable via the people that make up the fanbases of individual manga, so Oricon should still be a serviceable tool for comparing volumes of the same series. Comparing the performances of different series using Oricon weekly charts seems like riskier business, though; there’s a real chance that anything less than a factor-of-2 difference is due to the buying habits of their respective fans, rather than a difference in the actual amount of money they make their publisher.