Instituto Brasileiro de Geografia e Estatística

As of the release of the Quarterly Accounts of the third quarter of 2017, on December 1, 2017, the process of seasonal adjustment of the time series of the Quarterly Accounts, published by the IBGE, will be improved.

In the cases in which the X-13 ARIMA-SEATS pinpoints an ARIMA model suitable to the time series, the process will not be changed, remaining the pickmdl method currently used.

In the cases in which the X-13 ARIMA-SEATS does not pinpoint any adjustment model suitable to the projection of the final point of the time series, a second option of decomposition of the time series, established by the automdl method, will be tested.

Until then, in the cases in which the first model option faces problems – like auto-correction of residuals or super-differentiation –, an alternative pickmdl model to that tested in the first attempt – additive or multiplicative – is tested.

With the increasing size of the time series, the use of the automdl begins to present a higher stability in the selection of models, which qualifies its use as the best option to deal with cases in which the model selected by the pickmdl faces problems.

Directorate of Surveys
September 27, 2017