References must follow the APA Publication Manual exactly (APA, 1994). Students are encouraged to add citations to the Reference list at the time they are written into the text of any chapter. If the task of compiling the reference list is put off until last, the student may face the unhappy dilemma of being unable to locate a source that has been cited. Index cards help beautifully here. 

There must be a one to one correspondence between the references cited in the text and those cited in the reference list. References not cited are typically not included in the list.