susan wapner joins us, professor of real estate and finance at the university of pennsylvania's whartonchool of business. welcome, susan. nice to have you back with us. >> hi, susan. >> how problematic is this longer-term for the housing market? >> well, this will persist if current conditions, and the current conditions look like they will, for some time going forward. this means demand across the board for durables associated with home buying are not part of the expansion. and, in fact, our economic expansion has been slower than otherwise, because of the lack of demand for household formation and for housing on the part of millennials. so i have see this persisting in the next years to come. >> there are a lot of factors in here. it's delayed marrying, later. delayed household formation. income-related. incomes aren't what they were. credit standards very much tougher since the great recession. on what do you lay most of the responsibility for this delayed embracing of housing? >> well, it's certainly the economics. and the economics most important is rents and housing prices have in