# cffilter

## Syntax

## Description

The `cffilter`

function applies the Christiano-Fitzgerald filter to
separate one or more time series into additive trend and cyclical components.
`cffilter`

optionally plots the series and trend component, with
cycles removed.

In addition to the Christiano-Fitzgerald filter, Econometrics Toolbox™ supports the Baxter-King (`bkfilter`

), Hamilton
(`hfilter`

), and
Hodrick-Prescott (`hpfilter`

) filters.

`[`

returns tables or timetables containing variables for the trend and cyclical components
from applying the Christiano-Fitzgerald filter to each variable in an input table or
timetable. To select different variables to filter, use the
`TTbl`

,`CTbl`

] = cffilter(`Tbl`

)`DataVariables`

name-value argument.

`[___] = cffilter(___,`

specifies options using one or more name-value arguments in
addition to any of the input argument combinations in previous syntaxes.
`Name=Value`

)`cffilter`

returns the output argument combination for the
corresponding input arguments. For example, ```
cffilter(Tbl,Symmetric=true,Drift=[false false
true],DataVariables=1:3)
```

applies the symmetric Christiano-Fitzgerald filter to
the first three variables in the input table `Tbl`

, and removes the
linear drift term from the third variable before applying the filter.

`cffilter(___)`

plots time series variables in the
input data and their respective smoothed trend components (cycles removed), computed by
the Christiano-Fitzgerald filter, on the same axes.

`cffilter(`

plots on the axes specified by `ax`

,___)`ax`

instead of
the current axes (`gca`

). `ax`

can precede any of the input
argument combinations in the previous syntaxes.

## Examples

## Input Arguments

## Output Arguments

## More About

## Tips

The definition of a business cycle in [1]
suggests values in the table for the cutoff periods `LowerCutoff`

and
`UpperCutoff`

, and lag length `LagLength`

that depend
on the periodicity of the data.

Periodicity | `LowerCutoff` | `UpperCutoff` | `LagLength` |
---|---|---|---|

Yearly | 2 | 8 | 3 |

Quarterly | 6 | 32 | 12 |

Monthly | 18 | 96 | 36 |

In practice, use vectors of cutoff periods and lag lengths to test alternatives. Use the
plot produced by `cffilter`

to compare results among settings.

## References

## Version History

**Introduced in R2023a**