Real versus Nominal National Income

Idea

The same GDP or GNI figure can be stated in nominal or real terms, and in aggregate or per capita terms. Which is used decides whether the figure reflects a genuine change in output and well-being or merely a change in prices or population.

Mechanism

• Nominal national income is measured at current, prevailing market prices, with no adjustment for price changes — it does not discount inflation.

• Real national income is measured at constant (base-year) prices, removing the effect of price changes. It is obtained by deflating the nominal figure with the GDP deflator, a price index for total output:

$\text{Real data} = \frac{\text{Nominal data}}{\text{GDP deflator}} \times 100\%$

A convenient approximation links the two growth rates: $\text{Real growth} \approx \text{Nominal growth} - \text{Inflation rate}$.

• Per capita data divides the aggregate by population, $\text{Real data per capita} = \dfrac{\text{Real data}}{\text{Population}}$, giving the average per head.

Considerations

The distinction matters because nominal figures can move for reasons unrelated to output. A high nominal GDP under rapid inflation can conceal a falling real GDP — the standard cautionary case being a hyperinflation, where nominal output soars while real output collapses. Likewise, aggregate real GDP can rise while real GDP per capita falls if population grows faster than output. These are precisely the traps that make comparing standards of living with raw national income statistics unreliable.