Something I find silly about Book 5 - Real Estate writing, justify, statements, stocks, Estate

Howd

How does CFAI justify all their conclusive statements in the text about real estate - "Adding REITS to a portfolio of stocks and bonds increases return", "Adding direct real estate...decreases return, but increases Sharpre", etc..... WHEN THEY USE THE 1990-2004 TIME PERIOD AS THEIR BASIS.

Geez... don't they read their own writing? Where is the caution over time period bias?? They happen to cite a lengthy period of a freakin' real estate bubble, that happens to end three years before a historic real estate crash, and use the evidence as conclusive data.

I just remember laughing at this in my first read through and in the subsequent few reviews.