Market Interest Rates: Rising interest rates generally decrease bond prices, as newly issued bonds offer higher yields, making older bonds less attractive.

Inflation Expectations: Higher inflation expectations erode the real value of future bond payments, causing prices to fall to compensate for this diminished purchasing power.

Creditworthiness of Issuers: If the perceived creditworthiness of the entities issuing the bonds in SBMAX's portfolio deteriorates, investors demand higher yields, leading to lower bond prices.

Economic Growth: Strong economic growth can lead to increased inflation expectations and higher interest rates, both of which negatively impact bond prices.

Supply and Demand: Increased supply of similar bonds in the market can depress prices, while strong investor demand can support or increase prices.

Liquidity: Lower liquidity of the bonds in the fund's portfolio can result in wider bid-ask spreads and potential price discounts when selling.

Maturity Dates: Bonds with longer maturities are more sensitive to interest rate changes, thus have greater volatility.

Federal Reserve Policy: Changes in monetary policy, like adjusting the federal funds rate or quantitative easing, influence interest rates and thus bond prices.