Hi,
With MBS we do not use Delta. MBS is not like a stock. Every bond is different: FNMA?, Freddie?, GNMA?...30y 20y, 15yr collateral?.. Geography distribution?, dates of origination?, history of prepayments?. And thats just straight pools. MReits also buy CMOs which are a another subset in the MBS universe. A pool of pools if you will cut into different slices or tranches that all behave differnetly under different interest rate scenarios ( intentionally)
Price volatility and modified duration vary by pool and by tranche.
A plain vanilla approach would be that the longer the maturity or the lower the coupon the more price volatile. but its more about the cashflows.
For example a 20yr pool of 3.50% mortgages originated
this year will have much more price volatility than a pool of 30yr pool of 5.50% mortgages originated in 2007.
Because those 5.50's will be refying like a mofo.
Then you have to consider how much of a premium was paid. If the pool is paying fast the premium will be amortized faster eating into your yield.
I hope this helps.
I will teach you about MBS if you guys help me with options....