# Life Table Construction

### Description

Life tables are constructed from either numbers of individuals of a cohort alive at the start of an age interval (nx) or number of individuals of a cohort dying during the age interval (dx).

### Usage

1 |

### Arguments

`age` |
vector of age intervals (e.g., 0 to maximum cohort age). |

`numbers` |
number of individual alive (nx) or dead (dx) |

`r` |
known rate of increase (r) for methods 3 and 4 |

`type` |
numeric value of method to use to calculate life table. 1 = Age at death recorded directly and no assumption made about population stability or stability of age structure - Method 1 in Krebs (1989). 2 = Cohort size recorded directly and and no assumption made about population stability or stability of age structure - Method 2 in Krebs (1989). 3 = Ages at death recorded for a population with stable age distribution and known rate of increase - Method 5 in Krebs (1989). 4 = Age distribution recorded for a population with a stable age distribution and known rate of increase - Method 6 in Krebs (1989). |

### Details

Following Krebs (1989:413-420), standard life tables are calculated given age intervals and either cohort size or deaths.
X=age interval, nx=number of individuals of a cohort alive at the start of age interval X, lx = proportion of individuals surviving at the start of
age interval X, dx = number of individuals of a cohort dying during the age interval X,
qx=finite rate of mortality during the age interval X to X+1, px=finite rate of survival during the age interval X to X+1,
ex=mean expectation of life for individuals alive at start of age X.
For method 5, dx is corrected for population growth by *dx'=dx*exp(r*x)* and in method 6, nx is corrected for the same by *nx*e(r*x)*.
See Krebs for formulae.

### Value

Dataframe containing life table values.

### Author(s)

Gary A. Nelson, Massachusetts Division of Marine Fisheries gary.nelson@state.ma.us

### References

Krebs, C. J. 1989. *Ecological Methodologies*. Harper and Row, New York, NY. 654 p.

### Examples

1 2 |

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