cyEffTest {ChainLadder} | R Documentation |

## Testing for Calendar Year Effect

### Description

One of the three basic assumptions underlying the chain ladder method is the independence of the accident years. The function tests this assumption.

### Usage

```
cyEffTest(Triangle, ci = 0.95)
```

### Arguments

`Triangle` |
cumulative claims triangle. Assume columns are the development
period, use transpose otherwise.
A (mxn)-matrix |

`ci` |
confidence interval. Default: .95. A confidence interval is a type of interval estimate, computed from the statis tics of the observed data, that might contain the true value of an unknown population parameter. The interval has an associated confidence level that quantifies the level of confidence that the parameter lies in the interval. |

### Details

The main reason why this independence can be violated in practice is the fact that there could be certain calendar year effects such as major changes in claims handling or in case reserving or external influences such as substantial changes in court decisions or inflation.

As described by the Mack's 1994 paper a procedure is designed to test for calendar year influences.

The procedure returns a summary statistic `Z`

which is assumed to be Normally Distributed. It is therefore possible to define a confidence interval threshold in order to evaluate the outcome of the test.

### Value

cyEffTest returns a list with the following elements

`test_table` |
complete table of results |

`Z` |
summary statistic |

`E` |
expected value of the resulting distribution |

`Var` |
variance of the resulting distribution |

`Range` |
vector of the range corresponding the confidence interval threshold selected |

`ci` |
confidence interval |

### Note

Additional references for further reading:

Thomas Mack. Distribution-free calculation of the standard error of chain ladder reserve estimates. *Astin Bulletin*. Vol. 23. No 2. 1993. pp.213:225

Thomas Mack. The standard error of chain ladder reserve estimates: Recursive calculation and inclusion of a tail factor. *Astin Bulletin*. Vol. 29. No 2. 1999. pp.361:366

### Author(s)

Marco De Virgilis devirgilis.marco@gmail.com

### References

Mack, T., Measuring the Variability of Chain Ladder Reserve Estimates, *Casualty Actuarial Society Forum*, Spring 1994

### See Also

See also `qpaid`

for dealing with non-square triangles,
`dfCorTest`

for the test for correlations between subsequent development factors,
`chainladder`

for the chain-ladder method,
`summary.cyEffTest`

,
`plot.cyEffTest`

### Examples

```
# Before actually applying the Chain Ladder technique it is necessary to check
# wether the triangle has Calendar Year Effect
# Apply the function to the triangle and save the output into the variable test
test <- cyEffTest(RAA)
# Plot the confidence interval and the test metric
plot(test)
# The metric is within the confidence interval, therefore the triangle doesn't
# have Calendar Year Effect
# Print the summary table
summary(test)
# Print only the main outcomes
print(test)
# The test has returned a negative outcome. This means that the triangle is
# not affected by Caledar Year Effect and therefore the chain ladder method
# can be applied.
```

*ChainLadder*version 0.2.18 Index]