1) This is, as it says at the top, a public diary of my research in progress. I freely share the data as I assemble it, including the underlying spreadsheets, so that anyone else can build on it. If you don't like my analysis, do your own and share that, too. The aim is to collectively improve the data and analysis until it's good enough to publish either in my book or elsewhere. All this is released under a Creative Commons license, which means that anyone can use it as they see fit as long as they point back here. Indeed, USA Today did just that for that last post.
2) There's definitely an opportunity to make a better data-driven case that the blockbuster era has peaked. I very much look forward to other people (perhaps some who don't have a looming book deadline) grinding through the literature, building the spreadsheets and blogging the results. In the meantime, I'll do what I can.
Right now, I'm midway through the process of normalizing the Top 150 album data by total industry sales in each year, so it's more of an apples-to-apples comparison over the years. One problem is that I can't find total industry sales for years prior to 1990 (those since then are here). Can anyone point me to any figures? Even a few data points in the 70s or 80s would be helpful to calibrate the curve.
I did find another useful resource, the RIAA's database of Gold (over 500,000 sold), Platinum (1-2 million), Multi-Platinum (2-10 million) and Diamond (10 million and up) albums since 1958. The RIAA introduced Platinum in 1976, Multi-Platinum in 1984, and Diamond in 1999. I ran queries for each year and compiled the numbers, combining all four categories. I now know better than to say that the statistics speak for themselves, but they certainly are interesting:
Again, the spreadsheet is here.
A few methodological notes. As an album goes up the charts, it gets a Gold, then a Platinum, then a Multi-Platinum and so on. So a single album may show up several times in a chart like this that combines all four categories. That tends to amplify the height of the curve after the 80s, when such multi-award winners became more common, but not wildly so: total industry sales roughly parallel that rise.
One of the benefits of this multiple award process is that it allows us to look at a question that commentors raised in the last post: do older albums simply have more time to become a hit, something that would bias this kind of analysis against newer albums? The answer appears to be no. If you go through the database you'll see that albums that achieved Platinum or Multi-Platinum designation almost all did so within a year of going Gold. So most of the sales do seem to be in the first year or two after release.