Driveway [Heavy] [38 or 24]

Titanic sinking (1912): economic cost $7.5M (adjusted to $170M at today's values)
Cause: the central propeller wouldn't reverse

Chelsea FC buying Fernando Torres: economic cost £33.5M ($56M) (bought from Liverpool at £50M, current worth £16.5M)
Cause: Fernando Torres sucks

Mars Climate Orbiter crash: economic cost $330M
Cause: 2 groups worked on it and one group measured everything in metric and the other measured everything in silly imperial units and the measurements weren't exact enough

Zapmeister buys bitcoins: economic cost $4 billion
Cause: I bought bitcoins when bitstamp was at $775 and then sod's law says that whenever I buy something hoping the price goes up, the price will fall. Naturally if I hadn't bought anything the price would still be at least that much right now. Cost is the difference in market cap.

Tons of other financial errors: see here (seriously it's a pretty interesting read through)

Now, let's measure the impact of misrating the difficulties of ffr songs. I'm going to focus specifically on the misrating of Driveway [Heavy]; even though there may have been others as well, this serves as a good example.

Driveway [Heavy] was released in July 2007. It was rated an 8 on the old scale, which is 34+ (I think) on the new scale. Now 34 compared to where I think it should be which is 24 or 25 is a pretty huge difference, huge enough to send shock waves through financial markets, as we will shortly see. What else happened in July 2007? Well, just have a read through this: 2007-08 financial crisis. Is it certain that the rating of this ffr song caused it? Read the first sentence of the article:

Worst year since the 1930s? That means that out of over 70 possible years since then that the "worst one" could have taken place in, it happened in the same year as the mis-rating of Driveway [Heavy]. That's significant at the 2% level! Conclude that there is strong evidence to support that the mis-rating of the ffr song caused this financial crisis.

It's hard to estimate the financial impact of this crisis, but from skimming through the wikipedia article, it talks about one of the effects being the US bear market 2007-09, and in that article it mentions
$14 TRILLION! That's several orders of magnitude bigger than all the mistakes I talked about in the first part of this post. Now it's probably unfair to assume that all of it was due to FFR songs being mis-rated, but let's just say arbitrarily that it was responsible for one percent of that, because I'm feeling generous. Still, $140 billion is something you can't just blink at and move on.

What else? Oh yeah there was that 2007 bank run on Northern Rock and those other financial institutions that I can't be bothered to figure out but wikipedia says
$2.8 trillion losses. Again assuming a responsibility factor of one percent that's $28 billion, dwarfing all the other numbers up there.

I could go on but I think I've made my point. The point is that the global financial crisis of recent times could well have been either prevented or significantly lessened if this song had been rated a borderline 6/7.

On June 8th, 2012, about a month before I started playing this game, you guys changed all the difficulty ratings to the 1-99 scale, making the scale of the misjudgement in rating much more precise, as you issued it a 38 rating, way higher than the minimum 8 threshold of 34. Since that's an increase of only four points, you'd expect it to be responsible for another catastrophic financial blunder, but a smaller one. Here [pdf] is a list of all the natural disasters occurring worldwide during the month alone of June 2012. Note again the opening paragraph:
Yep, $1 billion, and all of this is the responsibility of the ffr difficulty system (will prove this later but for now take it on assumption). Also if you look further into the article you see that damage costs in the USA just for that month alone were about $4 billion, and another $4 billion for the rest of the world. See? That's what you get for misrating ffr songs.

What else? Have a read through the wikipedia about the 2012-2014 North American drought. Naturally it started only shortly after the change in the difficulty rating system. What was its economic impact?
That's not a very informative statistic, because $75 is 9 orders of magnitude smaller than $150 billion! But at least you can make a sensible guess that the actual value would be likely to be at least 10% of the way up, so like, $15 billion? That sounds like a reasonable number for messing with the ffr difficulty system.

What about Hurricane Sandy? Well that happened much later, so we can assume - and I'm being generous here - a 1% responsibility factor. Nicking the numbers out of the article, that's another $0.62 billion caused by misrating this ffr song.

I'm too lazy to add these numbers up but the whole point is that misrating ffr songs, especially (but not limited to) this one, is responsible at least in a pretty large part for screwing over world economy and causing several billions of dollars worth of losses worldwide.

Oh, I almost forgot, proof of responsibility. Well this article says
That's a p-value of about 6%. Make of that what you will - it's certainly less convincing than the 2% in the first one but it'll certainly flag up as significant on quite a few tests. So yeah, that's pretty convincing proof.