Bond yields do have an inverse relationship with their price. This is a direct mathematical relationship. I'll use a single bond as an example, and not a bond fund. This example is also
As an example, say you have a bond that pays $10 in annual interest. If you paid $100 for that bond, you'd get a 10% yield. If prevailing interest rates increase to 12%, the price you could sell the bond for would be $83.33. If you sold the bond, you would lose $16.67.
Of course, the bond market is BIG. Much bigger than the stock market. And there are different things that drive bond prices. There are many days where prices on some bonds will go up and prices on others will go down.
Some general rules of thumb:
-Bonds with long maturities are much more volatile than shorter term bonds. They also carry higher yields.
-Bonds with higher default risk are also more volatile, and will carry higher yields. However, these bonds sometimes move the opposite direction as the rest of the market, as default risk can fall faster than underlying rates can rise.
-Higher expected inflation will cause rates to rise and prices to fall.