Unlike investment return, there are no full proof quantitative measures of investment risk. Risk can only be qualitatively judged. It’s like driving a vehicle. One can choose between safe and rash driving. Driving at 100 kmph can be both rash and safe depending on type of vehicle, road and traffic. Similarly, a 20% return can be both safe and risky depending on the buying price. An expensive buy can get more expensive and generate that 20% return. At the same time a cheaper stock can get reasonably priced and generate 20% return. Former is risky, latter is less so.
Assessment of investment performance is incomplete if the focus is only on returns and not risks. The best way to reduce investment risk is to invest within one’s circle of competence and not to overpay.