Risk adjusted returns is defined as the ROI / Risk. Where risk is calculated as the changeability (volatility) of ROI. This is officially known as the Sharpe Ratio.
In this chart I`ve used a 4 year HODL period to run the Sharpe Ratio calculation, this seems a sensible choice as it is sufficient time to cover a full bear to bull cycle for Bitcoin.
Bitcoin: Coin Metrics
Gold: London Bullion Market
US Stocks: (SP500) Seeking Alpha and US Federal Reserve
Others: US Federal Reserve