Sometimes an author writes about research that someone else has done, but you are unable to track down the original research report. In this case, because you did not read the original work, you will include only the source you did consult in the Works Cited list.
The abbreviation “qtd.” in the parenthetical reference indicates you have not read the original research.
(Author Surname qtd. in Author Surname [of the source you did read] page number)