Inflation Expectations: TIIHX invests in Treasury Inflation-Protected Securities (TIPS). The price of TIPS, and thus TIIHX, is heavily influenced by expectations of future inflation. Higher inflation expectations generally lead to higher TIPS prices and vice versa.

Real Interest Rates: Real interest rates, which are nominal interest rates minus inflation, affect TIPS prices. Rising real interest rates typically cause TIPS prices to fall, as investors demand a higher yield to compensate for the inflation protection.

Treasury Yields: Changes in overall Treasury yields, particularly those of similar maturities to the TIPS held by TIIHX, can affect its price. Rising Treasury yields can put downward pressure on TIPS prices.

Market Demand for Inflation Protection: Investor appetite for inflation protection impacts the demand for TIPS. Increased demand can drive up TIPS prices and the value of TIIHX.

Economic Growth: Strong economic growth can lead to higher inflation expectations, positively impacting TIPS. Conversely, economic slowdowns can dampen inflation expectations, reducing TIPS prices.

Federal Reserve Policy: The Federal Reserve's monetary policy decisions, such as interest rate adjustments and quantitative easing, significantly influence inflation expectations and Treasury yields, thereby impacting TIPS prices.