Interest Rates: Rising rates typically decrease MBSAX's value as newer bonds offer higher yields, making existing lower-yielding bonds less attractive.

Mortgage Refinancing: Increased refinancing activity reduces MBSAX's holdings' average life, decreasing their value as principal is returned earlier than anticipated.

Prepayment Speeds: Faster prepayment speeds, influenced by economic conditions and interest rate movements, negatively impact MBSAX's performance.

Credit Risk: Deterioration in mortgage borrowers' creditworthiness can lower MBSAX's value due to potential defaults or delinquencies.

Economic Growth: Strong economic growth usually leads to higher interest rates, affecting MBSAX negatively. Conversely, a weak economy can lower rates, potentially boosting its value.

Inflation: Higher inflation expectations generally push interest rates upward, thus reducing MBSAX's value.

Federal Reserve Policy: The Federal Reserve's monetary policy, including quantitative easing or tightening, impacts interest rates and mortgage-backed security prices.

Supply and Demand: Market imbalances, such as an oversupply of mortgage-backed securities or decreased investor demand, can depress MBSAX's price.