The best way to support your opinion, as you know, is to present relevant facts
and figures. Facts and figures, however, are not so convincing if we don't tell
the reader their source, because authority is important. Facts and figures gotten
from hearsay, for example, has little authority, because hearsay is just what
you heard in conversation. Facts or figures from a Time Magazine article, on
the other hand, will have more authority, and the reader will be more likely
to believe them.
We cite sources differently in journalistic and essay writing from the way
we cite them in academic writing. For academic writing, the source's name, the
date, the publication source, the publisher, and more details about the source
are required. In journalistic and essay writing, though, we usually use more
informal methods, mentioning the source only in general terms, such as the expert's
name or position, or the publication in which we found the information.
Here are some examples of conventional methods of casual citation.
Note in the above samples that the reader is given some idea of the age of the information. Even item 4 implies that the information is current because the writer used present tense for says.