Data Interpretation
Data Interpretation gives a table, bar chart, line graph, pie chart, or caselet and asks for shares, percentage change, averages, ratios, and comparisons. The arithmetic is easy; marks are lost in reading the data and choosing the base.
Working rules
- Read the title, units, and scale before touching a number; note whether values are in thousands, lakhs, or percentages.
- Percentage change = change divided by the original value, times 100, where the original is the earlier or reference figure.
- A percentage point difference is not a percentage difference: 45% to 50% is 5 percentage points but an 11.1% relative rise.
- In pie charts, each slice is a share of the total; convert the angle to a fraction (angle divided by 360) or the percentage to an amount.
- Prefer cancellation and approximation: compare 47/63 with 52/70 by cross-multiplying rather than computing decimals.
- In caselets, extract only the figures the question needs.
Worked example
A survey of 1,200 respondents gives 35% to option A and 20% to option B. Difference = 15% of 1,200 = 180 respondents. Ratio A : B = 35 : 20 = 7 : 4.
Traps
- Using the later year as the base when the question asks for growth from the earlier year.
- Confusing percent with percentage points.
- Reading a broken axis as though it began at zero.
- Answering with absolute figures when the question asks for share or ratio.
- Averaging the averages of unequal groups.
- Comparing two ratios by their numerators only.