But classifying crypto as an investment is complicated, too. It doesn’t quite fit the mold of a traditional stock or bond, and while cryptocurrencies do share characteristics of commodities like gold — they can be bought and sold for cash and as derivatives based on expected future value — they have no inherent physical value or use.
Non-Bitcoin cryptocurrencies are collectively known as “altcoins” to distinguish them from the original.

Transactions are internet-based and are recorded in a blockchain. The blockchain shows the transaction history for each unit and is used to prove ownership. The digital assets are best visualized as virtual tokens. These tokens mean something to the internal system and can be programmed to record financial transactions and other valuable information.
In order to provide a methodology to detect bubbles in time series, Phillips, Wu, and Yu [23] proposed the supremum augmented Dickey-Fuller (SADF) test. This applies a series of right-tailed unit root tests to expanding windows of a time series (with a fixed start date), defined by where r2 is the final data point to be considered in each window, starting at r0 which is a fraction representing the smallest allowed window size and expanding to 1(the complete data set).