GDPt1

GDPt1 is a time-series concept used in macroeconomic data to denote the level of gross domestic product in a preceding period relative to a reference point. In many data sets, GDPt1 corresponds to GDP(t-1), the value of GDP one period earlier. The notation is not universal, however, and some sources may interpret GDPt1 differently, so it is important to consult the data documentation. GDPt1 is commonly described as lagged GDP or a one-period lag of the GDP series.

The variable can be measured in real terms (constant prices) to reflect volume changes, or in nominal terms (current prices) to reflect price levels. For econometric work, GDPt1 is typically used in real terms and at the same frequency as the period of analysis (quarterly or annual). When constructing GDPt1 from a GDP series, it is obtained by shifting the series by one period, with the first observation lacking a lag.

Common uses include modeling growth dynamics and persistence: as a lagged regressor in autoregressive specifications, in Okun-type equations, or in business cycle analyses. Growth rates based on GDPt1 use GDP(t-1) as the base, for example growth_t = (GDP_t / GDP(t-1)) - 1.

Data sources include national statistical offices, central banks, and international organizations such as the OECD, World Bank, and IMF. Revisions, seasonal adjustment, base-year changes, and differences in measurement (real vs nominal) can affect GDPt1 values and comparability across series.

See also GDP, real GDP, lag, autoregression, and Okun's law.