Portfolio management

Please expand on of the statements/questions below:
Portfolio measurement answers three questions; 1) return on the assets, 2) Why the portfolio has returned in the way it has, and 3) how performance can be improved.
Now, Explain, in detail, how you would approach measuring portfolio performance. Extend your discussion beyond a simple list, by providing detailed measures you would use in the process and why.
Note: Do not use Wikipedia, Investopedia or similar sources, as these sites are not considered academic sources.
Cite your source(s)