Description Usage Arguments Details Value Author(s) References See Also Examples

Computes a ‘combined forecast’ from a pool of individual model forecasts using trimmed mean at each point in time.

1 |

`x` |
An object of class |

`trim_factor` |
numeric. Must be between 0 (simple average) and 0.5 (median). |

`criterion` |
If |

Suppose *y_t* is the variable of interest, there are *N* not perfectly collinear predictors,
*f_t = (f_{1t}, …, f_{Nt})'*. For each point in time, the order forecasts are
computed:

*(f_t)_ord = (f_{(1)t}, …, f_{(N)t})'*

Using a trim factor *λ* (i.e., the top/bottom *λ \%* are trimmed) the combined forecast is calculated as:

*\hat{y}_t = 1/(N*(1-2λ)) ∑_{i = λ N +1}^{(1-λ)N} f_{(i)t}*

The trimmed mean is an interpolation between the simple average and the median. It is an appealing simple, rank-based combination method that is less sensitive to outliers than the simple average approach, and has been proposed by authors such as Armstrong (2001), Stock and Watson (2004), and Jose and Winkler (2008).

This method allows the user to select *λ* (by specifying `trim_factor`

), or to leave the selection to
an optimization algorithm – in which case the optimization criterion has to be selected (one of "MAE", "MAPE", or "RMSE").

Returns an object of class `foreccomb_res`

with the following components:

`Method` |
Returns the used forecast combination method. |

`Models` |
Returns the individual input models that were used for the forecast combinations. |

`Weights` |
Returns the combination weights obtained by applying the combination method to the training set. |

`Trim Factor` |
Returns the trim factor, |

`Fitted` |
Returns the fitted values of the combination method for the training set. |

`Accuracy_Train` |
Returns range of summary measures of the forecast accuracy for the training set. |

`Forecasts_Test` |
Returns forecasts produced by the combination method for the test set. Only returned if input included a forecast matrix for the test set. |

`Accuracy_Test` |
Returns range of summary measures of the forecast accuracy for the test set. Only returned if input included a forecast matrix and a vector of actual values for the test set. |

`Input_Data` |
Returns the data forwarded to the method. |

Christoph E. Weiss and Gernot R. Roetzer

Armstrong, J. S. (2001). Combining Forecasts. In: *Armstrong, J. S. (Ed.), Principles of Forecasting. Springer, Boston, MA*, 417–439.

Jose, V. R. R., and Winkler, R. L. (2008). Simple Robust Averages of Forecasts: Some Empirical Results. *International Journal of Forecasting*, **24(1)**, 163–169.

Stock, J. H., and Watson, M. W. (2004). Combination Forecasts of Output Growth in a Seven-Country Data Set. *Journal of Forecasting*, **23(6)**,
405–430.

`foreccomb`

,
`plot.foreccomb_res`

,
`summary.foreccomb_res`

,
`comb_SA`

,
`comb_MED`

,
`accuracy`

1 2 3 4 5 6 7 8 9 10 11 12 13 14 | ```
obs <- rnorm(100)
preds <- matrix(rnorm(1000, 1), 100, 10)
train_o<-obs[1:80]
train_p<-preds[1:80,]
test_o<-obs[81:100]
test_p<-preds[81:100,]
## User-selected trim factor:
data<-foreccomb(train_o, train_p, test_o, test_p)
comb_TA(data, trim_factor=0.1)
## Algorithm-optimized trim factor:
data<-foreccomb(train_o, train_p, test_o, test_p)
comb_TA(data, criterion="RMSE")
``` |

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