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In economics, nominal value is measured in terms of money, whereas real value is measured against goods or services. A real value is one which has been adjusted for inflation, enabling comparison of quantities as if the prices of goods had not changed on average. Changes in value in real terms therefore exclude the effect of inflation. In contrast with a real value, a nominal value has not been adjusted for inflation, and so changes in nominal value reflect at least in part the effect of inflation.

## Commodity bundles, price indices and inflation

A commodity bundle is a sample of goods, which is used to represent the sum total of goods across the economy to which the goods belong, for the purpose of comparison across different times (or locations).

At a single point of time, a commodity bundle consists of a list of goods, and each good in the list has a market price and a quantity. The market value of the good is the market price times the quantity at that point of time. The nominal value of the commodity bundle at a point of time is the total market value of the commodity bundle, depending on the market price, and the quantity, of each good in the commodity bundle which are current at the time.

A price index is the relative price of a commodity bundle. A price index can be measured over time, or at different locations or markets. If it is measured over time, it is a series of values ${\displaystyle P_{t}}$ over time ${\displaystyle t}$.

A time series price index is calculated relative to a base or reference date. ${\displaystyle P_{0}}$ is the value of the index at the base date. For example, if the base date is (the end of) 1992, ${\displaystyle P_{0}}$ is the value of the index at (the end of) 1992. The price index is typically normalized to start at 100 at the base date, so ${\displaystyle P_{0}}$ is set to 100.

The length of time between each value of ${\displaystyle t}$ and the next one, is normally constant regular time interval, such as a calendar year. ${\displaystyle P_{t}}$ is the value of the price index at time ${\displaystyle t}$ after the base date. ${\displaystyle P_{t}}$ equals 100 times the value of the commodity bundle at time ${\displaystyle t}$, divided by the value of the commodity bundle at the base date.

If the price of the commodity bundle has increased by one percent over the first period after the base date, then P1 = 101.

The inflation rate ${\displaystyle i_{t}}$ between time ${\displaystyle t-1}$ and time ${\displaystyle t}$ is the change in the price index divided by the price index value at time ${\displaystyle t-1}$:

${\displaystyle i_{t}={\frac {P_{t}-P_{t-1}}{P_{t-1}}}}$

${\displaystyle ={\frac {P_{t}}{P_{t-1}}}-1}$

expressed as a percentage.

## Real value

The nominal value of a commodity bundle tends to change over time. In contrast, by definition, the real value of the commodity bundle in aggregate remains the same over time. The real values of individual goods or commodities may rise or fall against each other, in relative terms, but a representative commodity bundle as a whole retains its real value as a constant from one period to the next.

Real values can for example be expressed in constant 1992 dollars, with the price level fixed 100 at the base date.

goods, which is used to represent the sum total of goods across the economy to which the goods belong, for the purpose of comparison across different times (or locations).

At a single point of time, a commodity bundle consists of a list of goods, and each good in the list has a market price and a quantity. The market value of the good is the market price times the quantity at that point of time. The nominal value of the commodity bundle at a point of time is the total market value of the commodity bundle, depending on the market price, and the quantity, of each good in the commodity bundle which are current at the time.

A price index is the relative price of a commodity bundle. A price index can be measured over time, or at different locations or markets. If it is measured over time, it is a series of values ${\displaystyle P_{t}}$ over time ${\displaystyle t}$.

A time series price index is calculated relative to a base or reference date.

A time series price index is calculated relative to a base or reference date. ${\displaystyle P_{0}}$ is the value of the index at the base date. For example, if the base date is (the end of) 1992, ${\displaystyle P_{0}}$ is the value of the index at (the end of) 1992. The price index is typically normalized to start at 100 at the base date, so ${\displaystyle P_{0}}$ is set to 100.

The length of time between each value of ${\displaystyle t}$ and the next one, is normally constant regular time interval, such as a calendar year. ${\displaystyle P_{t}}$ is the value of the price index at time ${\displaystyle t}$ after the base date. ${\displaystyle P_{t}}$ equals 100 times the value of the commodity bundle at time ${\displaystyle t}$, divided by the value of the commodity bundle at the base date.

If the price of the commodity bundle has increased by one percent over the first period after the base date, then P1 = 101.

The inflation rate ${\displaystyle i_{t}}$ between time ${\displaystyle t-1}$ and time ${\displaystyle t}$ is the change in the price index divided by the price index value at time ${\displaystyle t-1}$:

${\displaystyle i_{t}={\frac {P_{t}-P_{t-1}}{P_{t-1}}}}$

expressed as a percentage.

## Real value

The nominal value of a commodity bundle tends to change over time. In contrast, by definition, the real value of the commodity bundle in aggregate remains the same over time. The real values of individual goods or commodities may rise or fall against each other, in relative terms, but a representative commodity bundle as a whole retains its real value as a constant from one period to the next.

Real values can for example be expressed in constant 1992 dollars, with the price level fixed 100 at the base date.

The nominal value of a commodity bundle tends to change over time. In contrast, by definition, the real value of the commodity bundle in aggregate remains the same over time. The real values of individual goods or commodities may rise or fall against each other, in relative terms, but a representative commodity bundle as a whole retains its real value as a constant from one period to the next.

Real values can for example be expressed in constant 1992 dollars, with the price level fixed 100 at the base date.

constant 1992 dollars, with the price level fixed 100 at the base date.

The price index is applied to adjust the nominal value ${\displaystyle Q}$ of a quantity, such as wages or total production, to obtain its real value. The real value is the value expressed in terms of purchasing power in the base year.

The index price divided by its base-year value ${\displaystyle P_{t}/P_{0}}$ gives the grow

The index price divided by its base-year value ${\displaystyle P_{t}/P_{0}}$ gives the growth factor of the price index.

Real values can be found by dividing the nominal value by the growth factor of a price index. Using the price index growth factor as a divisor for converting a nominal value into a real value, the real value at time t relative to the base date is:

The real growth rate ${\displaystyle r_{t}}$ is the change in a nominal quantity ${\displaystyle Q_{t}}$ in real terms since the previous date ${\displaystyle t-1}$. It measures by how much the buying power of the quantity has changed over a single period.