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Half Life

In a pool of mortgages underlying a mortgage-backed security, the length of time it takes for half the aggregate principal to be repaid. A half life is normally about 12 years, but this may vary depending on how often homeowners refinance their mortgages (which pays off all principal at once). Half lives are calculated for mortgage-backed securities issued or guaranteed by Freddie Mac, Fannie Mae, and Ginnie Mae.

Weighted Average Life

The amount of time for the principal on a loan or a mortgage to be paid off. The length of the weighted average life depends on the amount of principal paydowns and how often they are made. Once the WAL is calculated, one can determine how long it will take to pay off half of the remaining principal.


The length of time before half the principal on a debt is expected to be repaid through amortization or sinking fund payments. For example, a 25-year bond issue may require the issuer to retire 5% of the beginning principal commencing 5 years after the issue date. Thus, the bond issue has a half-life of 5 years plus the number of years required to retire half the issue, or 15 years. Mortgage-backed securities often have a relatively short half-life because many homeowners pay off or refinance their mortgages early. Also called average life.
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Although missing the human-like qualities that comprise Half-Life 2's Alyx Vance, Wikipedia reported Cortana has been recognized in the Halo series by her sex appeal, believability and character depth.
To determine the relationship between (1) initial recovered DCD concentrations and half-life of DCD, and (2) weather and soil microclimate and half-life of DCD, Pearson correlation analysis was applied.
Half-life of a learning curve is the incremental production level required to reduce cumulative average cost per unit to half of its initial level.
The individual half-life values appear reasonable and give an average value of 1.
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Patent and Trademark Office has issued Xencor a broad patent covering optimized monoclonal antibody variants and their application for extending in vivo half-life of antibodies.
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This experiment will help students understand the concept of a half-life, or the time is lakes for a radioactive substance to lose half its radioactivity.
The authors report that the average covariate-adjusted average rate of decrease in serum PFOA concentration after water filtration was 26% per year [95% confidence interval (CI), 25-28% per year], consistent with a median serum PFOA half-life of 2.
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