Federal Funds Rate: MMSKX is a money market fund. Its yield, and thus price (NAV usually stays at $1), is heavily influenced by the Federal Funds Rate. When the Fed raises rates, MMSKX's yield typically increases, making it more attractive.

Short-Term Interest Rates: Changes in short-term interest rates, beyond just the Fed Funds Rate, also affect MMSKX. Treasury bill rates, commercial paper rates, and other money market instruments directly impact the fund's returns.

Demand for Safe Assets: Increased demand for very safe, liquid assets can drive more investment into money market funds like MMSKX. This influx of cash may slightly impact the fund's ability to maintain its yield.

Credit Risk Perception: Even though money market funds invest in very high-quality debt, changes in the perceived credit risk of issuers in the money market (like banks or corporations) can have a minor effect.

Fund Expense Ratio: The expense ratio of MMSKX directly impacts the net yield investors receive. A higher expense ratio means a slightly lower net return for the investor.

MMSKX Portfolio Holdings: The specific mix of securities held within MMSKX’s portfolio affects the overall yield the fund can generate. Different instruments yield slightly different returns.

Economic Conditions: Overall economic health affects interest rate expectations and demand for safe assets, thus indirectly influencing MMSKX. Strong growth might lead to higher rates, vice versa.