Avoid citing secondary sources where possible. Always try and read the original source.
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 report, you will include only the source you did consult in your References.
The words “as cited in” in the parenthetical reference indicate you have not read the original research.
In-text citation (paraphrase)
Fong’s 1987 study (as cited in Bertram, 1996) found that older students’ memory can be as good as that of young people, but this depends on how memory is tested.
Do not include Fong (1987) in your References; do include Bertram (1996)
Author Surname, First Initial. Second Initial [of the source you read]. (Year). Book title: Subtitle. Place of Publication: Publisher.