Bitcoin 'Misery Index'

Looks like it's just another data-mined modification of Relative Strength Index (RSI) applied to bitcoin.

Here is the wikipedia on RSI: https://en.wikipedia.org/wiki/Relative_strength_index

Some variations of RSI factor in volatility which this guy's Bitcoin version appears to do.

Worth saying here, there is no empirical evidence for indexes indicators like these or the million other versions of it to have any basis in reality for predicting price movement reliably. Pretty obvious Bitcoin markets in 2011 were nothing like Bitcoin markets in 2017. Said another way "Sometimes I trade bitcoin but I only buy on Tuesdays, my best friend only buys bitcoins on Thursdays, and my performance trading Bitcoin is better than my friend's. So Tuesdays are the best time to buy Bitcoin, see previous sentence for evidence why". Also this article from investopedia appears to be another sponsored marketing content not a journalism article.

Forbes says "It is a numerical index that ranges from 0 to 100 and incorporates the win-ratio, or percentage of days that Bitcoin is up, and the upside less downside volatility."

https://www.forbes.com/sites/chuckjones/2018/03/10/the-bitco...

More importantly, why is it assumed to average to 0?

Via the power of wishful thinking.