Index Numbers | Class 11 Economics Notes

3. CONSTRUCTION OF AN INDEX NUMBER

This section explains the principles and methods of constructing index numbers, focusing primarily on price index numbers. It begins with a simple example showing different percentage changes in prices of commodities and highlights the difficulty in summarizing these changes individually. The section introduces two main methods for constructing index numbers: the aggregative method and the method of averaging relatives. The simple aggregative price index is calculated as the ratio of the sum of current period prices to the sum of base period prices, multiplied by 100. However, this simple method treats all items equally without considering their relative importance or weights, which limits its usefulness. To address this, the weighted aggregative price index incorporates weights, typically quantities from the base or current period, reflecting the relative importance of each item. The section introduces Laspeyre's price index, which uses base period quantities as weights, and Paasche's price index, which uses current period quantities as weights, explaining their interpretations and differences. The method of averaging relatives involves calculating price relatives (ratios of current to base prices) for each commodity and then averaging them, either simply or weighted by expenditure shares. The section provides detailed numerical examples for each method, illustrating the calculations and interpretations of the resulting index numbers. It also discusses the choice of weights and the practical considerations in constructing meaningful index numbers.

📊 Diagram: Includes tables showing commodity prices and quantities for base and current periods, illustrating calculation steps for different index formulas. Visual depiction of baskets of goods and their price changes to explain weighting.

🧪 Activity: Interchange current and base period values in Example 2 data and calculate price indices using Laspeyre's and Paasche's formulas. Observe differences from earlier results.

🔗 Connection: Prepares for the next section that discusses important types of index numbers used in economics.