U.S. Copyright law is complex, and made more complicated by digital publishing. More detailed information on copyright and scholarly publishing can be found in the Copyright Guide. Copyright as it pertains to data, however, is fairly straightforward.
It is important to observe the distinction between copyrighted works and intellectual property. Copyright applies to original works in a fixed medium. According to 17 U.S.C. §102b, "In no case does copyright protection [...] extend to any idea [...] concept, principle, or discovery." Copyright does not apply to ideas, research data, or factual information. The Supreme Court case Feist Publications v. Rural Telephones further asserted that copyright law is intended to protect "original creative expression, not just hard work."
You can own copyright of expressions of data, such as graphs or charts included in a publication, but the underlying factual information presented in the graph or chart is not copyright.
Where copyright law does not cover data, researchers may pursue other avenues to protecting their intellectual property, such as filing patents or protecting trade secrets. Non-disclosure agreements, grants, contracts, institutional policies, federal and state laws (such as HIPAA or FERPA) may all affect the decisions and protections you are afforded in this area.
Making Decisions About Your Research Data video by Nancy Sims, University Copyright Librarian at the University.