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Index Number

Gujarat Board · Class 12 · Statistics

Quick revision notes for Index Number — Gujarat Board Class 12 Statistics. Key concepts, formulas, and definitions for last-minute revision.

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Key Topics to Revise

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1. Definition and Meaning of Index Number

  • An index number is the percentage relative change in the value of a variable in the current period compared to its value in the base (reference) period.
  • Two methods to measure change: (1) Absolute measure (difference) — NOT always appropriate because it ignores base values; (2) Relative measure (ratio) — APPROPRIATE because it accounts for the base va
  • Price relative of an item = (Current year price / Base year price) × 100
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2. Characteristics and Uses of Index Number

  • INDEX NUMBER IS UNIT-FREE: Since it is a ratio (relative measure), the units cancel out. This allows comparison of items measured in different units (kg, litre, metre, etc.).
  • INDEX NUMBER IS A COMPARATIVE MEASURE: It compares values at two different time periods through ratio.
  • INDEX NUMBER IS A SPECIAL AVERAGE: It possesses all characteristics of an average — it summarizes a large dataset into a single representative value.
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3. Base Year — Fixed Base Method and Chain Base Method

  • BASE YEAR: A normal, stable year free from unusual events (flood, drought, war, strike, pandemic) used as a reference. Index value of base year = 100.
  • FIXED BASE METHOD: One specific stable year is selected as base year for ALL years in the series. All comparisons are made with this single base year.
  • CHAIN BASE METHOD: The base year CHANGES for each current year. Each year's index is computed relative to the IMMEDIATELY PRECEDING year.
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4. Conversion Between Fixed Base and Chain Base Index Numbers

  • WHEN TO CONVERT: (1) Fixed → Chain Base: When you need to study SHORT-TERM changes from fixed base data. (2) Chain → Fixed Base: When you need to compare a year's value to a SPECIFIC past year from ch
  • CONVERSION FORMULA (Fixed → Chain): CBI of current year = (FBI of current year / FBI of previous year) × 100
  • CONVERSION FORMULA (Chain → Fixed): FBI of current year = (CBI of current year × FBI of previous year) / 100

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Key Concepts

An index number is the percentage1Index numbers serve as economic indicators**Definition**Definition

Frequently Asked Questions

What are the important topics in Index Number for Gujarat Board Class 12 Statistics?
Key topics in Index Number include Index Number – Complete Chapter Overview, Which Formula to Use? — Index Number Decision Tree, Index Number - Complete Chapter Overview. These are the concepts Gujarat Board Class 12 examiners draw on most — study them first, then practise related questions.
How to score full marks in Index Number — Gujarat Board Class 12 Statistics?
Start by understanding all key concepts. Practise previous year questions from this chapter. Revise formulas and definitions regularly. Use flashcards for quick revision before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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