It asks which bonds effective duration will lengthen if interest rates rise:

The options are an option free bond, callable bond and a putable bond.

I get that a putable bond is in the money as interest rates rise so the effective duration decreases. The answer is Callable Bond and it is true that the effective duration will lengthen but so does the Option free bond. I always thought as interest rates rise for a callable bond the price change would match that of a straight bond. In the answer it says the effective duration of an option free bond changes very little in response to interest rate movements.

That makes little sense to me because the effective duration for a straight bond is always greater then the effective duration for a callable or putable bond.

I must be misreading something but I’m not getting this.