mbsyield2oas

Option-adjusted spread given yield

Syntax

OAS = mbsyield2oas(ZeroCurve, Yield, Settle, Maturity, IssueDate,
GrossRate, CouponRate, Delay, Interpolation PrepaySpeed,
PrepayMatrix)

Arguments

ZeroCurve

A matrix of three columns:

  • Column 1: Serial date numbers.

  • Column 2: Spot rates with maturities corresponding to the dates in Column 1, in decimal (for example, 0.075).

  • Column 3: Compounding of the rates in Column 2. Values are 1 (annual), 2 (semiannual, 3 (three times per year), 4 (quarterly), 6 (bimonthly), 12 (monthly), and -1 (continuous).

Yield

Mortgage yield, compounded monthly (in decimal).

Settle

Settlement date (scalar only). A serial date number or date string. Date when option-adjusted spread is calculated. Settle must be earlier than Maturity.

Maturity

Maturity date. Scalar or vector in serial date number or date string format.

IssueDate

Issue date. A serial date number or date string.

GrossRate

Gross coupon rate (including fees), in decimal.

CouponRate

(Optional) Net coupon rate, in decimal. Default = GrossRate.

Delay

(Optional) Delay (in days) between payment from homeowner and receipt by bondholder. Default = 0 (no delay between payment and receipt).

Interpolation

Interpolation method. Computes the corresponding spot rates for the bond's cash flow. Available methods are (0) nearest, (1) linear, and (2) cubic spline. Default = 1. See interp1 for more information.

PrepaySpeed

(Optional) Relation of the conditional payment rate (CPR) to the benchmark model. Default = end of month's CPR. Set PrepaySpeed to [] if you input a customized prepayment matrix.

PrepayMatrix

(Optional) Customized prepayment matrix. A matrix of size max(TermRemaining)-by-NMBS. Missing values are padded with NaNs. Each column corresponds to a mortgage-backed security, and each row corresponds to each month after settlement.

All inputs (except PrepayMatrix) are number of mortgage-backed securities (NMBS) by 1 vectors.

Description

OAS = mbsyield2oas(ZeroCurve, Yield, Settle, Maturity, IssueDate, GrossRate, CouponRate, Delay, Interpolation, PrepaySpeed, PrepayMatrix) computes the option-adjusted spread in basis points.

Examples

expand all

Calculate the Option-Adjusted Spread of a 30-Year Fixed-Rate Mortgage Pool

Calculate the option-adjusted spread of a 30-year, fixed-rate mortgage pool with about 28-year weighted average maturity left, given assumptions of 0, 50, and 100 PSA prepayments. First, create the bonds matrix:

Bonds = [datenum('11/21/2002')  0        100  0  2  1;
         datenum('02/20/2003')  0        100  0  2  1;
         datenum('07/31/2004')  0.03     100  2  3  1;
         datenum('08/15/2007')  0.035    100  2  3  1;
         datenum('08/15/2012')  0.04875  100  2  3  1;
         datenum('02/15/2031')  0.05375  100  2  3  1];

Choose a settlement date.

Settle = datenum('20-Aug-2002');

Assume the following clean prices for the bonds:

Prices =  [ 98.97467;
            98.58044;
           100.10534;
            98.18054;
           101.38136;
            99.25411];

Use the following formula to compute spot compounding for the bonds:

SpotCompounding = 2*ones(size(Prices));

Compute the zero curve.

[ZeroRatesP, CurveDatesP] = zbtprice(Bonds, Prices, Settle);
ZeroCurve = [CurveDatesP, ZeroRatesP, SpotCompounding]
ZeroCurve =

   1.0e+05 *

    7.3154    0.0000    0.0000
    7.3163    0.0000    0.0000
    7.3216    0.0000    0.0000
    7.3327    0.0000    0.0000
    7.3510    0.0000    0.0000
    7.4185    0.0000    0.0000

Assign the following parameters:

Price         = 95;
Maturity      = datenum('02-Jan-2030');
IssueDate     = datenum('02-Jan-2000');
GrossRate     = 0.08125;
CouponRate    = 0.075;
Delay         = 14;
Interpolation = 1;
PrepaySpeed   = [0 50 100];

Compute the yield, and from the yield, compute the option-adjusted spread.

[mbsyld, beyld] = mbsyield(Price, Settle, ...
Maturity, IssueDate, GrossRate, CouponRate, Delay, PrepaySpeed);

OAS = mbsyield2oas(ZeroCurve, mbsyld, Settle, ...
Maturity, IssueDate, GrossRate, CouponRate, Delay, ...
Interpolation, PrepaySpeed)
OAS =

   26.0508
   28.6355
   31.2232

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