A new index tracking the performance of 240 digital currencies will let investors take the temperature of the crypto market

• An index from S&P Dow Jones launched on Tuesday aims to give investors a snapshot of the overall crypto market.
• The index will be top-heavy: bitcoin and ethereum currently make up 62.8% of the crypto market.
• The broader crypto market has tended to move in tandem with the big two mega-cap coins, according to Insider's analysis of the S&P crypto indices.

An index from S&P Dow Jones launched on Tuesday aims to give investors a unified snapshot of the overall crypto market as institutional players grow more curious about crypto.

The S&P Cryptocurrency Broad Digital Market Index tracks 240 cryptocurrencies worth over $10 million that meet a few baseline requirements for inclusion. While S&P has previously created indices for bitcoin and ethereum, the new measure will offer a wider lens for the crypto ecosystem.

The index will be somewhat top-heavy. Bitcoin and ethereum currently make up 62.8% of the total crypto market, according to CoinMarketCap, and the top 10 cryptocurrencies account for 82%.

By contrast, the top two stocks in the S&P 500, Apple and Microsoft, comprise just 11% of the index. The top 10 stocks make up just over a quarter of the S&P 500, at 27.9%.

S&P Dow Jones also announced several sub-indices, including ones that track the crypto market without the impact of bitcoin and ethereum.

The broader crypto market has tended to move in tandem with the big two mega-cap coins. The 238 top cryptocurrencies excluding bitcoin and ethereum are strongly correlated with an index of only bitcoin and ethereum, according to Insider's analysis of the S&P crypto indices. (The correlation coefficient was 0.76 and considered data from February 2017, when the indices begin.)

S&P Dow Jones hopes its new indices will bring transparency to an often opaque space that is nevertheless attracting widespread institutional interest.

"The expansion of our Digital Market Indices family gives one of the broadest snapshots yet of this rapidly growing asset class with the ability to slice and dice by market cap," said Peter Roffman, head of innovation and strategy at S&P Dow Jones, in a statement.