Forecasting Central Government Primary Expenditure: A Comparative Analysis of Econometric Techniques, Machine Learning, Deep Learning, and Forecast Combination..
forecasting. time series. fiscal policy.
The forecasting of public expenditures is essential for fiscal planning and the sustainability
of government accounts. However, many countries, especially those with low and
middle incomes, still rely on subjective methods and simple spreadsheet extrapolations
for fiscal forecasts. Despite the growing use of traditional econometric methods, the
application of machine learning and deep learning techniques remains limited and largely
concentrated on forecasting public revenues. International studies show gains from using
machine learning and deep learning algorithms, particularly due to their ability to handle
nonlinearities and complex patterns. However, robust evidence is still lacking for short
and noisy monthly fiscal series, which are common in emerging countries. In the Brazilian
context, there is a scarcity of research focused on disaggregated forecasting of federal
primary expenditures and systematic comparisons across different classes of models. This
work empirically investigates the predictive performance of traditional models, machine
learning models, deep learning models, and model combinations in forecasting monthly
series of Brazilian federal expenditures. To this end, we combined statistical benchmarks
and supervised algorithms, performing automatic hyperparameter optimization to obtain
robust point forecasts. We used temporal cross-validation as a model selection procedure
and conformal prediction to generate calibrated confidence intervals. Various error metrics
were employed to compare the performance of the approaches. Overall, statistical
models proved highly competitive, outperforming machine learning and deep learning
algorithms. Although inter-class ensembles did not minimize average errors, they increased
the robustness of the forecasts. Based on official data from the Federal Government, this
study demonstrated that time series forecasting techniques are an important tool to
support the work of fiscal policy makers. Future research may explore exogenous variables
and structural or semi-structural models to enhance the accuracy, robustness, and
interpretability of predictive models.