What type of information should members refrain from acting upon, as it could affect investment value?

Members should refrain from acting upon material nonpublic information, as it can significantly affect investment value and is often subject to legal restrictions. This type of information is specifically defined as information that could influence an investor's decision but hasn't been made available to the general public. Acting on such information can lead to insider trading violations, which not only undermine market integrity but also carry legal penalties.

The prohibition against using this kind of information is central to maintaining fair and transparent markets. It ensures that all investors have equal access to pertinent information before making investment decisions.

In contrast, public information is readily available to everyone and can be used freely by investors. Confidential information, while sensitive, does not necessarily have the immediate potential to impact the investment's value in the same direct way as material nonpublic information. Historical data is past information and does not have the capacity to affect the present investment decisions based on unknown factors. Therefore, the focus on material nonpublic information is crucial in the context of fiduciary duty and ethical investing practices.