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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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A strength of our approach is that our estimates of intrinsic PCB elimination half-lives have a broad empirical base.
Although these factors may influence apparent elimination half-lives (Milbrath et al.
PFHS), which could account for the varied half-lives of elimination across species.
Pharmacokinetic modeling of saturable, renal resorption of perfluoroalkylacids in monkeys-probing the determinants of long plasma half-lives.
OBJECTIVE: The goals of our study are to clarify the interpretation of half-lives derived from fitting exponential functions to declining CSTD and to provide a method of estimating human elimination half-lives from CSTD collected in a postban situation.
CSTD-derived half-lives have also been referred to as "human half-life" (Woodruff et al.
The influence of human metabolic half-lives on CBAT shape was evaluated for a hypothetical chemical of log [K.
5) according to three different metabolic half-lives (1, 15, and 50 years) and three hypothetical emission scenarios represented by bell-shaped functions that increased and decreased over 30, 50, and 100 years, respectively (Figure 3).
The objective of the present study was to calculate the apparent half-lives for BDE-209 and other higher BDEs in human serum, using data from occupationally exposed workers sampled before, during, and after a vacation period.
Data from these samplings were not included in the modeling of half-lives but are reported separately.
Table 1 shows similar average half-lives for persons < 12 and < 18 years of age, and a significantly longer half-life for persons > 18 years of age.
Hoffman would like to extend her chemical investigations to elements with a higher atomic number (a large number of protons) than hahnium, but the half-lives of known isotopes of elements 106, 107, 108 and 109 --sighted but not yet named -- are 0.