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BANKERS TUTORIAL · RBI · TOPIC & REVISION GUIDE

Topic guide: Base effects: the denominator behind annual inflation

Base effects arise when the earlier observation used for a percentage comparison is unusually high or low. Annual inflation can change because the comparison base changes, even when the recent price-index movement appears modest.

01 / 03Learn with a clear direction

2 min read Original learning material · Prepared 14 Oct 2026

This is an independent topic guide, not the official syllabus. Compare it with the current paper outline and rules published by the examination authority.

01 / UNDERSTANDING

Learning objectives

Cover annual versus sequential growth, denominator alignment and the difference between an arithmetic contribution and a causal explanation. Align current and year-earlier observations in two clearly labelled columns. Your practical tasks are to align each observation with its year-earlier base and calculate annual and sequential changes separately. These conceptual objectives are a study framework, not an official question allocation. Demonstrate the distinction with a fresh worked case, including the assumptions that make the answer valid.

02 / UNDERSTANDING

The concept in context

Base effects arise when the earlier observation used for a percentage comparison is unusually high or low. Annual inflation can change because the comparison base changes, even when the recent price-index movement appears modest. Write both the current observation and the year-earlier denominator before interpreting an annual rate.

03 / UNDERSTANDING

A worked learning case

At one comparison date an invented index is 120 against a year-earlier 100, giving 20% annual inflation. At the next date it is 121 against an earlier base of 110, giving 10%. The current index has risen from 120 to 121, yet the annual rate has dropped because the comparison base is substantially higher.

ORIGINAL EDUCATIONAL PRACTICE

Try it before you check.

What is the second annual inflation rate in the example?

Show the answer and reasoning

10%.

The second comparison uses 121 as the current index and 110 as the year-earlier base. Their difference is 11, and 11 divided by 110 equals 10%. Comparing 121 with 100 would use the wrong period. The lower annual rate can coexist with a rise in the current index.

Two traps to watch for.

  • Using the previous month as the base for an annual comparison.
  • Treating a favourable base effect as proof of falling current prices.

YOUR TOPIC-SPECIFIC LEARNING MAP

Your revision map

  1. Align each observation with its year-earlier base.

  2. Calculate annual and sequential changes separately.

  3. Explain the arithmetic before suggesting economic causes.

Explain the idea, apply it to a new situation, then check what changed in your reasoning.

BANKERS TUTORIAL · SOURCE NOTES

Keep the source alongside your notes.

Official links provide subject context and authoritative reference material. This guide’s explanation, scenario and question are original Bankers Tutorial learning content.

  1. ncert.nic.in https://ncert.nic.in/textbook.php?leec1=ps-6
  2. www.rbi.org.in https://www.rbi.org.in/scripts/DataDefinition.aspx

For RBI preparation, check the current official notice before relying on changing dates, rules or examination requirements.

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