Year-on-Year Comparison in Pie Chart with Examples
Year-on-Year Comparison in Pie Chart involves comparing the values represented by corresponding sectors in two different years. Convert sector angles into actual values when the total is given, or compare directly when values are provided. Percentage change, increase or decrease, and ratio calculations help solve these data interpretation problems accurately.
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What Is Year-on-Year Comparison in a Pie Chart?
If a category occupies an angle θ in a pie chart with total value T, its value is (θ/360) × T. For two years, calculate the value separately for each year and then compare them. Percentage change is calculated using the earlier year as the base: ((New value − Old value) / Old value) × 100.
Year-on-Year Comparison in Pie Chart Video Lessons
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Two Pie Charts Year-on-Year Comparison
Learn how to compare two pie charts representing different years, identify changes in category shares, and interpret year-on-year data accurately.
Year-on-Year Comparison in Pie Chart Formula & Tricks
Important Formulas
Use this formula when the pie chart gives a sector angle and the total quantity for that year.
A positive result indicates an increase, while a negative result indicates a decrease.
The absolute difference is found by taking the magnitude of this result when only the gap is required.
Reduce the ratio using the greatest common divisor of the two values.
Quick Tricks
If the totals for both years are equal, the ratio of category values is the ratio of their sector angles. No separate conversion to actual values is needed.
For year-on-year percentage change, always divide by the value in the earlier year. Dividing by the new year gives a different reverse percentage.
When the total values differ, compare (angle × total) for each year because the common divisor 360 is the same.
Year-on-Year Comparison in Pie Chart Concepts
Converting a Sector Angle into a Category Value
A full pie represents 360°. Therefore, a sector of θ° represents θ/360 of the total. For example, if a company records total sales of 1,200 units and a product occupies 90°, its sales are (90/360) × 1,200 = 300 units.
Comparing the Same Category Across Two Years
If the two pie charts have different totals, the same angle does not represent the same quantity. For year 1, use (θ₁/360) × T₁, and for year 2, use (θ₂/360) × T₂. Then compare the resulting values.
Calculating Percentage Increase or Decrease
If the old value is O and the new value is N, use ((N − O)/O) × 100. If N is greater than O, the result is an increase; if N is less than O, it is a decrease.
Comparing Pie Charts with Equal and Unequal Totals
For equal totals T, value ratio = angle ratio. For unequal totals, value ratio is (θ₁T₁):(θ₂T₂), because each category value is obtained by dividing angle × total by 360.
Year-on-Year Comparison in Pie Chart Visual Guide & Data
Use the table and chart below to understand the data better.
Illustrative Year-on-Year Category Data
Category values represented in two pie charts for 2023 and 2024.
| Category | 2024 value | 2023 value |
|---|---|---|
| A | 120 | 90 |
| B | 150 | 120 |
| C | 180 | 150 |
| D | 150 | 180 |
Note: The 2024 values are used as the primary values for the first pie-chart visual, and the 2023 values are used for the second visual. The table values are direct category quantities.
Category distribution in 2024
Category distribution in 2023
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Year-on-Year Pie Chart Revision Points
Use the earlier year as the base and convert each sector separately when chart totals differ.
- Category value = (sector angle/360°) × total value.
- Percentage change = (new value − old value) / old value × 100.
- A positive percentage shows an increase; a negative percentage shows a decrease.
- Compare sector angles directly only when the two pie-chart totals are equal.
- For unequal totals, calculate both actual category values before comparing.
- The sum of all sector angles in a pie chart is 360°.
- The sum of all category values equals the total represented by the pie chart.
Year-on-Year Comparison in Pie Chart FAQs
What is the year-on-year comparison in pie chart formula?
Percentage change = ((New year value − Old year value) / Old year value) × 100. The old-year value is always the denominator.
How do you find a value from a 120° sector in a pie chart with total 900?
Value = (120/360) × 900 = 300. Thus, the sector represents 300 units.
Can sector angles be compared directly when the pie-chart totals are different?
No. First calculate the actual values using (angle/360) × total. Direct angle comparison is valid only when both totals are equal.
A category rises from 160 to 200. What is its year-on-year increase?
The increase is 40. Percentage increase = (40/160) × 100 = 25%.
A category falls from 250 to 200. What is the percentage decrease?
The decrease is 50. Percentage decrease = (50/250) × 100 = 20%.
What is the value ratio for angles 45° and 75° in equal-total pie charts?
The ratio is 45:75 = 3:5. Equal totals allow the sector-angle ratio to represent the value ratio directly.