Yields are generally higher on an instrument for a few reasons when they are issued. first, tax treatment is a consideration. second, special features that may provide more risk than other securities. third, the overall risk of the issuer itself. coprs, for example, make quarterly payments much like dividends, but they are taxed as interest income and may therefore carry higher yields. but there may be other features that make the issuer more risky for the average investor. coprs, for example, often come with a deferred payment clause, whereby regular quarterly payments can accrue for a specified number of quarters. while you may find that with preferred shares, you wont find that with bonds and debentures. so a coprs investor could conceivably make their purchase and hold it for a few years and finally sell the investment without ever receiving a payment. its not likely but it could happen. its these kinds of considerations that may lead investors to demanding higher compensation for their investment funds.