QUOTE (Andy the Actuary @ Feb 18 2010, 08:42 AM)

Given my incredibly bad attitude regarding the interest rate constraints and accompanying irrationalities the feds have legislated over the years for lump sum calculations, I can honestly say that for most plans, I've recommended plan year stability period and 5 month lookback, which makes sense for planning purposes. The thought of averaging interest rates that do not relate to reality is repugnant. Thus, I've never been involved with a plan that averaged monthly interest rates for lump sum determination. Given my age, I likely never will. Therefore, I offer no thoughts on averaging segment rates.
In short, you have asked me if I believe in a supreme being. I said no. So, I can't nor will attempt to describe him, her, or it.
Oh, yee of little faith...how about Andy the Ayatollah of cynics??
Now for my own faith and cynicism:
I believe that the IRS will act in a consistent manner when the management of the IRS is stable and in control of their auditors. You could count on some regulators to keep a consistent policy position for an extended period of time. That is why we all hoped for consistent guidance from the Isadore Goodmans, Ira Cohens, Dick Wickershams, and Jim Hollands of the world.
I do not believe that market rates are stable, because there are too many counter examples. So an average of yield curves allows some stability in planning for distributions. A 30 yr treasury rate of 2.87% is just wacho!