What is a chain-linked index? Examine how its adoption alongside the fixed-base IIP addresses limitations of India's current industrial statistics.

A chain-linked index measures production changes by continuously updating item weights (annually or periodically) and linking successive short periods, rather than freezing the weight structure to a single distant base. The TAC-IIP report (2026), chaired by Dr. Mridul K. Saggar, recommended India adopt one alongside its fixed-base IIP as part of the 2011-12 → 2022-23 rebasing [1][2].

What a chain-linked index is

• Weights are refreshed with fresh survey data (e.g. Annual Survey of Industries) and periods are chained together [1].
• Captures the current structure of output, unlike a fixed base anchored to one year.

Limitations of the current fixed-base IIP it addresses

• Weight obsolescence: a base frozen at 2011-12 misrepresents today's industrial mix; chaining keeps weights contemporary [1].
• Substitution bias: fixed weights overstate old, declining industries; annual updates reduce this distortion [2].
• Emerging-sector blind spots: enables inclusion of new activities — rare earth minerals, gas and water supply, sewerage and waste management — within a 463 item-group basket [1].
• Comparability: aligns IIP with GDP, CPI and WPI base cycles, aided by the Geometric Mean linking method for continuity [2].

Residual concerns

• Chaining introduces "drift" and demands robust, timely source data and MoSPI–State DES coordination [1].

By retaining the fixed-base index for stable comparison while adding a chain-linked variant for structural realism, India moves its industrial statistics toward international best practice, strengthening evidence-based industrial and monetary policymaking.