One of the biggest financial stories of 2017 has been the seemingly unstoppable rise of bitcoin, which has more than tripled this year and seems to make new records by the day.

Such a rally has inevitably raised questions over whether there is a bubble in the digital currency, or in the broader space of cryptocurrencies, which earlier this week topped $100 billion in combined market capitalization. Breaking that milestone was largely due to bitcoin BTCUSD, +1.51% which by itself accounts for nearly half the value of the still-nascent sector. However, a new measure of bitcoin valuation, one based roughly on the price-to-earnings ratio applied to stock valuation, suggests that rally still has room to grow.