I. Introduction

The Seasonally Adjusted National Accounts (SANA) of the Philippines was first designated for generation and release in 1994 through the National Statistical Coordination Board (NSCB) Resolution No. 6, Series of 1994. By the virtue of Republic Act No. 10625, the Philippine Statistics Authority (PSA) was created to be the central statistical authority of the Philippine government on primary data collection. With this, the designation for generation and release of the SANA was later on adopted through the PSA Resolution No. 1, Series of 2017.

Through the Macroeconomic Accounts Service, the PSA, regularly releases the quarterly Gross Domestic Product (GDP) with the quarterly Seasonally Adjusted National Accounts (SANA) of the Philippines. The SANA presents the economic performance of the country without the influence of predictable seasonal patterns. It is a tool to identify the underlying trends revealing the true behavior of the series, compares quarter-on-quarter changes, and analyzes the seasonal effects in the series. It also provides early signals to the economic planners through quarter-on-quarter changes that will serve as a guide for better plans and decisions in maintaining the economic stability of the country.

The publication includes the Seasonally Adjusted GDP compiled at the production side and expenditure side. The GDP production and GDP expenditure and its components are compiled and presented by major industries and by major expenditure items including its details. The Seasonally Adjusted Net Primary Income and Gross National Income are also included.

II. Data and Data Sources

III. Methodology

III.1. Basic Framework

The Philippine Statistics Authority currently uses the internationally recommended seasonal adjustment method which is the X-13ARIMA-SEATS, a seasonal adjustment software program developed and maintained at the U.S. Census Bureau.

1. The X-13ARIMA-SEATS

The SEATS (Signal Extraction in ARIMA Time Series) seasonal adjustment method available in X-13ARIMA-SEATS uses parameter estimates from autoregressive integrated moving average (ARIMA) models to filter the series and derive the seasonal factors and other components.

The decomposition model for the series may be multiplicative or additive. The multiplicative model assumes dependence between the components therefore monthly seasonal factors for the multiplicative model are ratios with all positive values. Meanwhile, additive decomposition assumes independence of the components, thus seasonal factors may represent positive or negative deviations from the original series. The seasonally adjusted series may exhibit negative values depending on the resulting decomposition of the trend-cycle, seasonal, and irregular component.

2. Indirect Method for Seasonal Adjustment

In the Seasonally Adjusted National Accounts, the quarterly GDP is generated using Indirect Approach or by seasonally adjusting the 80 sub-industries and summing the seasonally adjusted components to produce indirect seasonal adjustment aggregates. Hence, the seasonally adjusted GDP is derived at the production side.

Moreover, the expenditure items are also seasonally adjusted independently and aggregated to major expenditure categories.

The seasonally adjusted Gross National Income is also derived by adding the seasonally adjusted GDP and Net Primary Income.

3. Quality Measures

Decomposition of the (preadjusted) series should be conducted using either the moving average X-11 method or the model-based SEATS method. The X-13ARIMA-SEATS program, which implements both X-11 and SEATS, is the recommended procedure for seasonal adjustment in the Quarterly National Accounts.

To examine the reliability of the estimates, the Quality Statistic (Q-statistic) is measured for each adjusted series.

IV. Concepts and Definition of Terms

1. A Time Series is a set of observations on a variable measured or recorded chronologically with equal intervals.

2. Seasonality (seasonal component) is a regular fluctuation with similar patterns and magnitude that repeatedly occur within a calendar year and normally observed for high frequency data such as monthly and quarterly series.

3. Seasonal adjustment is a statistical technique to remove the effects of seasonal calendar influences operating on a time series.

V. Dissemination of Results

The Seasonally Adjusted National Accounts is included in the PSA System of Designated Statistics, indicated to be released 40 days after the reference period, except Q4, which is to be released 30 days after the reference period. The following schedules are the releases of SANA based on the Advance Release Calendar of PSA:

The web release materials include press release, statistical tables, infographics, publication report, and social cards.

VI. Citation

Philippine Statistics Authority. (2023). Technical Notes on the Seasonally Adjusted National Accounts of the Philippines. https://psa.gov.ph/statistics/technical-notes

VII. Contact Information

Mr. Marck C. Pascasio 
Chief Statistical Specialist)
Expenditure and Integrated Accounts Division 
(02) 8376-1982 
m.pascasio@psa.gov.ph

For data request, you may contact: 
Knowledge Management and Communications Division 
(02) 8462-6600 loc. 820 
info@psa.gov.ph | kmcd.staff@psa.gov.ph