**2. Dual data imperatives**

#### **2.1 Keynesian GDP (K) and survival (S)**

The dollar denomination of variables counted in different units (automobiles, cereal boxes, etc.) allows the ratio scaling of GDP up to a multiplier calibrating GDP in single, thousands, millions, billions, or trillions of current US dollars.

This ratio scaling also allows daily exchange-rates to multiply one nation's currency into another's (e.g. dollars into yen). Likewise, the ratio scaling of life expectancy at birth allows survival to be scaled in days, months, years, or decades.

The goal of this paper is to relate GDP to survival by posing survival as a fractional-polynomial function of GDP. It is shown that this function predicts survival of the world population.

**Definition 1. K** denotes frequency-weighted Keynesian GDP. Vector **K** replicates **Kt** Nt times and contains ΣtNt values, where Nt is world population size in year t = 1990 … 2018.

**Definition 2. St** is survival time, denoted by life expectancy at birth in year t = 1990 … 2018.

**Definition 3.** Vector **S** replicates **St** Nt times and contains ΣtNt values, where Nt is world population size in year t = 1990 … 2018. **S** is a ratio scale unique up to multiplication by a positive constant that calibrates **S** in days, weeks, months, or years.
