How are the measurement units for a time series represented in Data Buffet and in basket downloads?
This content originally appeared in the April 2012 issue of Data Buffet Monthly, and has subsequently been adapted and updated.
Every economic time series in Data Buffet expresses a measurement, and measurements have units. We record the unit as metadata accompanying each series, as part of the textual description—specifically, as a parenthesized phrase at the end (the unit-descriptor), consisting of some combination of multiplier, base-unit, period, interval, and adjustment. For instance:
- Employment: Total nonagricultural, (Mil. #, SA)
- Bankruptcy: Personal - Total, (# 12-mo. EOP)
- Interest rates: Federal funds effective rate, (% p.a., NSA)
- Gross State Product: Total, (Bil. Ch. 2005 USD, SAAR)
- Government finance: Revenue, (Bil. ARS, SA)
- Consumer Price Index: All-items, (Index 1998=100, NSA)
Our most common base-units are count (#); a percentage of the whole (%) or per-annum percentage rate (% p.a.); a generic index (Index) or an index relative to a base period and value (Index 1982-84=100); and a currency level in nominal (USD), real (2005 USD) or chained (Ch. 2005 EUR) terms. We use three-letter ISO currency codes rather than symbols or local abbreviations (the symbol “$” for the U.S. dollar is a legacy that we are phasing out).
The base-unit can be multiplied or scaled, most commonly by thousands, millions or billions (Ths., Mil., Bil.) (using the American definition of billion, 1,000,000,000). The value might be measured over a prolonged period, such as year-to-date (YTD), a rolling period (12-mo.) or moving average (3-mo. MA), or at the end of the period (EOP).
The values may be raw, original or not seasonally unadjusted (NSA) or they may have undergone some form of adjustment to remove recurring patterns, as with seasonal adjustment (SA) or calendar adjustment (CDA). To facilitate comparison across different frequencies, it’s common to use an annual rate (AR); in particular, many of our forecast series are expressed at a seasonally adjusted annual rate (SAAR).
The unit-descriptor serves two purposes: how the indicator is measured, and what kind of math can be performed on it. For example, you can add currency levels, but not percent-changes; if the levels have different scales, you have to change to a common scale before adding; it's nonsense to apply a percent-change growth rate to something that is already a percent-change.
In complicated cases, we move part of the measurement outside the unit-descriptor, as the last clause in the text-descriptor. These include "share of" measurements with a complex or verbose denominator ("percent share of working-age women"), and commodity prices with a complex definition ("per dozen grade-A eggs"). In these cases, the unit-descriptor continues to serve the "what kind of math?" purpose.
For a list of common units and abbreviations, read more.
![[Screengrab of View mode with unit-descriptor circled]](https://www.economy.com/images/buffet/monthly_update/sgb_units_view.png)
Figure 1. Measurement units as displayed in View mode. The description appears in the gray header above the tabulation.
![[Screengrab of Mnemonic 411 with unit-descriptor circled]](https://www.economy.com/images/buffet/monthly_update/sgb_units_m411.png)
Figure 2. Measurement units as displayed in Mnemonic 411, on the sixth row of the Overview tab.
![[Screengrab of basket output with unit-descriptor circled]](https://www.economy.com/images/buffet/monthly_update/sgb_units_basket.png)
Figure 3. Measurement units as displayed in basket output, among the default metadata header fields, viewed in Microsoft® Excel 2010.