## reserving.TailConstant


A given tail factor, as chainladder-python's [TailConstant](reserving.TailConstant.md#prospicio.reserving.TailConstant).


Usage


``` python
reserving.TailConstant()
```


The factor applies from the attachment age to ultimate. Past the attachment it is spread over the following periods as `1 + x * decay**k`, the last factor making up the difference; this shapes the factors past the attachment, not the factor to ultimate. An attachment before the oldest age replaces the estimated factors from there.


## Parameters


`factor: float = ``1.0`  
Factor from the attachment age to ultimate; finite and positive.

`decay: float = ``0.5`  
Share of each period's development kept in the next, from 0 to 1.

`attachment_age: int`  
Age in months the factor attaches at (the first age at or after it); the oldest age by default. An age at or before the youngest replaces every estimated factor (chainladder-python ignores such an attachment).


## Examples

``` python
>>> from prospicio.reserving import ChainLadder, TailConstant, Triangle
>>> tri = Triangle.from_long([2020, 2020, 2021], [12, 24, 12], {"paid": [100.0, 150.0, 200.0]})
>>> fit = ChainLadder(tail=TailConstant(1.05)).fit(tri, "paid")
>>> fit.tail, round(fit.ultimate[1], 6)
```

(1.05, 315.0)


## Attributes

| Name | Description |
|----|----|
| [attachment_age](#attachment_age) | Age in months the factor attaches at; `None` is the oldest age. |
| [decay](#decay) | Share of each period's development kept in the next. |
| [factor](#factor) | Factor from the attachment age to ultimate. |

------------------------------------------------------------------------


#### attachment_age


Age in months the factor attaches at; `None` is the oldest age.


`attachment_age: int | None`


------------------------------------------------------------------------


#### decay


Share of each period's development kept in the next.


`decay: float`


------------------------------------------------------------------------


#### factor


Factor from the attachment age to ultimate.


`factor: float`