AskUs@CSS: APA, 6th edition

In APA style, an organization is considered a corporate author. In regards to your first citation, you would not use the acronym APTA, but spell out the full name -

American Physical Therapy Association. (2011).  Today’s physical therapist: A comprehensive review of a

     21st-century health care profession. Retrieved from http://www.apta.org/uploadedFiles/APTAorg/

     Practice_and_Patient_Care/PR_and_Marketing/Market_to_Professionals/TodaysPhysicalTherapist.pdf

I am not clear in your question if you want to know how to cite the author in a parenthetical (in-text) reference or if you are referring to the bibliographic management software EndNote. APA style does not use end-notes.

Depending on how you are writing your paper, a parenthetical reference would look something like this -

Physical therapy for pets is expected to grow exponentially in the next 10 years (American Physical Therapy Association, 2011).

or

"There is a great demand for physical therapy for retired agility dogs, such as the loyal and tireless Australian Shepherd" (American Physical Therapy Association, 2011, p. 24).

For more on in-text citations, see: http://libguides.css.edu/c.php?g=41681&p=265025

It is possible to use the acronym APTA is subsequent in-text citations. See the above guide page for details.

In regards to your second citation you have error in the author's name. If you scroll down to the bottom of the page you will see this statement: "A federal government managed website by the Centers for Medicare & Medicaid Services. 7500 Security Boulevard Baltimore, MD 21244"

Your your citation should be:

Centers for Medicare & Medicaid. (n.d.). By population. Retrieved from http://www.medicaid.gov/medicaid-chip-program-information/by-population/by-population.html

You have 2015 listed as a date, but I do not see it on the URL listed in the retrieval statement.

In-text references would be treated as in the first example.