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Data Comparison Across Years / Categories

Introduction

Many Data Interpretation (DI) problems ask you to compare values across years or categories to find growth, decline, or relative performance. This pattern is important because exam questions often require ranking, identifying fastest growth, or computing year-on-year changes.

Pattern: Data Comparison Across Years / Categories

Pattern

Compare absolute changes and percentage changes across the same base period to identify fastest/slowest growth or relative performance.

Key formulas:
Absolute change = New value - Old value
Percentage change = (New - Old) ÷ Old × 100

Step-by-Step Example

Question

The table below shows population (in thousands) of four cities in 2019 and 2021. Which city had the highest percentage growth from 2019 to 2021?

City2019 (’000)2021 (’000)
Alpha120132
Beta90108
Gamma150165
Delta8096

Solution

  1. Step 1: Compute absolute change for each city:

    Alpha: 132 - 120 = 12 (’000)
    Beta: 108 - 90 = 18 (’000)
    Gamma: 165 - 150 = 15 (’000)
    Delta: 96 - 80 = 16 (’000)

  2. Step 2: Compute percentage growth using 2019 as base:

    Formula: (New - Old) ÷ Old × 100

    Alpha: (12 ÷ 120) × 100 = 10.00%
    Beta: (18 ÷ 90) × 100 = 20.00%
    Gamma: (15 ÷ 150) × 100 = 10.00%
    Delta: (16 ÷ 80) × 100 = 20.00%

  3. Step 3: Compare percentage growth values:

    Beta and Delta both have the highest percentage growth of 20.00%.

  4. Final Answer:

    Beta and Delta (tie)

  5. Quick Check:

    Verify for Beta: (108 - 90) ÷ 90 = 18 ÷ 90 = 0.2 = 20% ✅

Quick Variations

1. Compare data across more than two years (use CAGR or year-on-year %).

2. Compare categories (e.g., product lines) using the same formulas - base can be first year or average depending on question wording.

3. When bases differ widely, use percentage change for fair comparison; use absolute change for unit-based differences.

Trick to Always Use

  • Step 1: Compute absolute change first to spot major movers.
  • Step 2: Convert to percentage using the correct base year: (New - Old) ÷ Old × 100.
  • Step 3: If there’s a tie in percentage, compare absolute changes if the question specifies “largest increase.”

Summary

Summary

In the Data Comparison Across Years / Categories pattern:

  • Calculate absolute change = New - Old to see raw difference.
  • Calculate percentage change = (New - Old) ÷ Old × 100 for proportional growth.
  • Always use the same base year for fair comparison.
  • Keep units (₹, %, ’000) consistent before comparing values.
  • Perform a quick verification for one entry to confirm accuracy.

Practice

(1/5)
1.

School Enrollment - Compare 2018 vs 2020

The table shows student counts in three streams for 2018 and 2020. Which stream had the highest percentage growth from 2018 to 2020?

Stream2018 (students)2020 (students)
Arts1,2001,440
Science1,5001,650
Commerce800880
easy
A. Arts
B. Science
C. Commerce
D. All equal

Solution

  1. Step 1: Compute absolute increases (2020 - 2018):

    Arts: 1,440 - 1,200 = 240 students.
    Science: 1,650 - 1,500 = 150 students.
    Commerce: 880 - 800 = 80 students.

  2. Step 2: Compute percentage growth using 2018 as base:

    Arts: (240 ÷ 1,200) × 100 = 20.00%.
    Science: (150 ÷ 1,500) × 100 = 10.00%.
    Commerce: (80 ÷ 800) × 100 = 10.00%.

  3. Step 3: Compare percentages:

    Highest percentage growth = Arts (20.00%).

  4. Final Answer:

    Arts → Option A.

  5. Quick Check:

    240 ÷ 1,200 = 0.20 → 20% ✅

Hint: Compute absolute change first, then convert to % by dividing by the older year's value.
Common Mistakes: Comparing absolute increases directly instead of percentage when bases differ.
2.

Company Revenues - 2019 vs 2021 (₹ lakh)

The table shows revenues of three companies in 2019 and 2021. Which company had the largest absolute increase in revenue from 2019 to 2021?

Company2019 (₹ lakh)2021 (₹ lakh)
X400500
Y350420
Z300360
easy
A. X
B. Y
C. Z
D. Tie between X & Y

Solution

  1. Step 1: Compute absolute increases (2021 - 2019):

    X: 500 - 400 = 100 (₹ lakh).
    Y: 420 - 350 = 70 (₹ lakh).
    Z: 360 - 300 = 60 (₹ lakh).

  2. Step 2: Identify largest absolute increase:

    Largest increase = 100 (₹ lakh) for Company X.

  3. Final Answer:

    X → Option A.

  4. Quick Check:

    100 > 70 > 60 ✅

Hint: When asked 'largest absolute increase' use raw differences (new - old) rather than %.
Common Mistakes: Mixing up absolute increase with percentage increase.
3.

Product Sales - Yearly Totals (₹ lakh)

The table shows sales of four products across three years. Which year had the highest total sales?

Product2019 (₹ lakh)2020 (₹ lakh)2021 (₹ lakh)
A120140160
B150160170
C8090100
D90100120
easy
A. 2019
B. 2020
C. Cannot determine
D. 2021

Solution

  1. Step 1: Sum totals for each year:

    2019 total = 120 + 150 + 80 + 90 = 440 (₹ lakh).
    2020 total = 140 + 160 + 90 + 100 = 490 (₹ lakh).
    2021 total = 160 + 170 + 100 + 120 = 550 (₹ lakh).

  2. Step 2: Compare yearly totals:

    2019 = 440; 2020 = 490; 2021 = 550 → highest = 2021.

  3. Final Answer:

    2021 → Option D.

  4. Quick Check:

    550 > 490 > 440 ✅

Hint: When asked about 'which year had highest total', sum columns year-wise and compare.
Common Mistakes: Comparing product-wise instead of year-wise totals.
4.

Vehicle Sales by Region - 2017 vs 2019

The table shows vehicle sales (units) in four regions for 2017 and 2019. Which region had the highest percentage growth from 2017 to 2019?

Region2017 (units)2019 (units)
North1,5001,650
South1,2001,560
East900990
West800880
medium
A. North
B. South
C. East
D. West

Solution

  1. Step 1: Compute absolute increases (2019 - 2017):

    North: 1,650 - 1,500 = 150.
    South: 1,560 - 1,200 = 360.
    East: 990 - 900 = 90.
    West: 880 - 800 = 80.

  2. Step 2: Compute percentage growth using 2017 as base:

    North: (150 ÷ 1,500) × 100 = 10.00%.
    South: (360 ÷ 1,200) × 100 = 30.00%.
    East: (90 ÷ 900) × 100 = 10.00%.
    West: (80 ÷ 800) × 100 = 10.00%.

  3. Step 3: Compare percentages:

    Highest percentage growth = South (30.00%).

  4. Final Answer:

    South → Option B.

  5. Quick Check:

    360 ÷ 1,200 = 0.30 → 30% ✅

Hint: When region sizes differ, percentage compares fairly - compute (new - old) ÷ old × 100.
Common Mistakes: Picking the region with largest absolute increase ignoring base sizes.
5.

Company Expenses by Category - 2018 vs 2020 (₹ lakh)

The table shows expenses under categories for 2018 and 2020. Which category recorded the highest percentage increase from 2018 to 2020?

Category2018 (₹ lakh)2020 (₹ lakh)
Sales100130
Admin6066
R&D4064
Marketing5070
medium
A. Sales
B. Admin
C. R&D
D. Marketing

Solution

  1. Step 1: Compute absolute increases (2020 - 2018):

    Sales: 130 - 100 = 30.
    Admin: 66 - 60 = 6.
    R&D: 64 - 40 = 24.
    Marketing: 70 - 50 = 20 (all in ₹ lakh).

  2. Step 2: Compute percentage growth using 2018 as base:

    Sales: (30 ÷ 100) × 100 = 30.00%.
    Admin: (6 ÷ 60) × 100 = 10.00%.
    R&D: (24 ÷ 40) × 100 = 60.00%.
    Marketing: (20 ÷ 50) × 100 = 40.00%.

  3. Step 3: Compare percentages:

    Highest percentage increase = R&D (60.00%).

  4. Final Answer:

    R&D → Option C.

  5. Quick Check:

    24 ÷ 40 = 0.6 → 60% ✅

Hint: Smaller bases can produce larger % growth - always compute percent after finding absolute change.
Common Mistakes: Choosing the largest absolute increase without considering base size.

Mock Test

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