Facts that are widely disseminated and commonly known require no attribution (see Chapter 5). Otherwise, credit the source of the fact in your speech:

According to the Galileo Project website (name), a project supported by Rice University (source qualifier), Galileo was appointed professor of mathematics at the University of Padua in 1592 (fact).

Statistics adds credibility to speech claims and can make your arguments more persuasive, if you tell listeners what the numbers actually mean, use terms that describe them accurately, and reveal the methods and scope of the research:

According to a nationally representative sample of males ages 15 and older, selected by a random digit sample of telephone numbers (methods and scope of research) conducted by the Pew Research Center, a major nonpartisan “fact tank” that provides information on the issues shaping America and the world (source qualifier), a record 8 percent of households with children are now headed by single fathers, up from just over 1 percent in 1960 (what the numbers actually mean).⁴