The traditional asset classes passive investors are most likely to select include: stocks, bonds, real estate, and cash.
Historically, real estate investments were relatively inaccessible, and they were categorized under alternative asset classes. In recent decades such investments have become far more accessible. Most doctors have real estate exposure though their primary residence and sometimes rental properties, and it’s become easy to invest directly in real estate investment trusts (REITs). Accordingly, we’ll view real estate as a traditional asset class.
More complex asset classes are known as alternative asset classes. These include hedge funds, private equity, venture capital, commodities, etc. Due to their complexity, opacity, illiquidity, volatility, and high fees, alternative asset classes should be avoided by most investors and in particular passive investors. In any case, they are mostly restricted to accredited investors.
 Accredited investors must prove they have a net worth of at least $1 million or show annual earnings of at least $200,000 for two years. There is legislation underway to reduce these requirements, making alternative asset classes accessible to more investors. It is uncertain whether this is a good idea.