July 8th, 2002, 10:41 pm
Standard desk practice for hedging swaps/swaptions is usually something like the following.First let's exclude options & subsequent vega risk.To obtain today's (LIBOR) yield curve, the swap desk has selected a set of N "stripping instruments" (for USD, the instrument set consists of Eurodollar deposits to the first future, 20 or so Eurodollar futures, the 6y, 7y, 10y, 15y, 20y, 25y, and 30y swap rates ... the exact set varies with institution & may include FRAs), and fed these to the stripper. From these instruments, the stripper determines the discount factor df(t), which is the value today of 1 dollar delivered on date t. Throughout the day, the instrument prices and swap rates are updated on a more or less continous basis.Knowing the discount factors, one can price any swap, either spot starting or forward starting, as well as FRAs, depositis, Eurodollar futures, amortizing swaps, ... ie, all the so called delta instruments that a swap trader may be dealing with. This means that the value of the swap book is a function of the N deposit rates, futures prices, swap rates, ... that went into the stripper. We now figure out our "bucket deltas:" for each instrument used in the stripper, we bump the rate/price of that instrument, re-strip the curve to find a new set of discount factors, and then re-price all deals in our book; the difference between this value and the base case is our bucket delta to that particular instrument. We then repeat for all instruments to get all our bucket deltas. The swap (delta) trader keeps track of all these risksand hedges them out bucket by bucket. He may leave, say, some 12y risk open, offsetting it with 10y and 15y risk, but this is the trader's call.The reason that futures are used in the front part of the curve is that the first 5 years of futures are quite liquid, and can be bought or sold freely without chewing up bid-ask spread.Options (caps, floors, swaptions, range notes, inverse floaters, Bemudans, exotics) are no different. To get the (bucket) delta risks, strips the yc to find the discount factors, and prices all the deals in the book(s) to get the base value. Then one-by-one, one bumps the stripping instruments, re-strips the curve, re-prices all the deals in the book(s), and subtract out the base value to get the book's risk to that particular stripping instrument.To hedge this risk, one simply hands it off to the swap trader, who consolidates it with the delta risks from the swap/FRAs/futures etc. in his book. Typically the swap trader is responsible for hedging these delta risks. Usually one has thousands of deals, and all there delta risk is expressed in terms of the 30 or so stripping instruments.To get the "gamma risk" in the swap world one usually executes a parallel shift of the yield curve by, say +10bps, and then determines the price and bucket deltas of the shifted curve. One then repeats this at, say, -10bps, +20bps, -20bps, etc. until one is comfortable.Can one do better by using factor analysis and hedging only the dominant motions instead of all possible movements? Maybe, but one is always leaving some risk open on the table unless the factors add up to 100% of the probability ... in fact one is taking a proprietary view. This is why it is the trader's call.