  Our study empirically predicts the bubble of non-fungible tokens (NFTs):
transferable and unique digital assets on public blockchains. This topic is
important because, despite their strong market growth in 2021, NFTs on a
project basis have not been investigated in terms of bubble prediction.
Specifically, we applied the logarithmic periodic power law (LPPL) model to
time-series price data associated with four major NFT projects. The results
indicate that, as of December 20, 2021, (i) NFTs, in general, are in a small
bubble (a price decline is predicted), (ii) the Decentraland project is in a
medium bubble (a price decline is predicted), and (iii) the Ethereum Name
Service and ArtBlocks projects are in a small negative bubble (a price increase
is predicted). A future work will involve a prediction refinement considering
the heterogeneity of NFTs, comparison with other methods, and the use of more
enriched data.
