What Is Data Interpretation?

Data interpretation is the process of reading data in tables, charts and graphs, working out what it shows, and using it to answer a question or make a decision. In aptitude tests, a data interpretation question gives you a table or chart and asks you to calculate something from it, such as a total, an average or a percentage change. The skill is finding the few figures that matter and using them correctly.

Data interpretation questions make up much of a typical free numerical reasoning test, so they are worth learning to do quickly.

What data interpretation means

Interpreting data has three parts:

1. Reading: understanding what the table or chart shows, including its title, labels, units and key.
2. Selecting: picking out only the figures the question needs.
3. Calculating and concluding: doing the arithmetic and checking the answer makes sense.

At work this is how people turn reports into decisions. A manager compares this quarter’s sales with last quarter’s, or a buyer works out which supplier gives the best price per unit. Tests use the same kind of material, in a timed, multiple choice format. Our guide to what numerical reasoning is explains how these questions fit into the wider test.

The kinds of data you will see

• Tables: rows and columns of figures. The most precise source, so answer from a table where you can.
• Bar charts: good for comparing categories. Read values against the axis carefully.
• Line graphs: show change over time. Check whether each point is a month, a quarter or a year.
• Pie charts: show shares of a total, usually as percentages. You often need the total from elsewhere to turn a share into a number.
• Text with figures: a line under a table may give an exchange rate, a fee or a growth forecast that the calculation depends on.

How to answer a data interpretation question

1. Read the question first. Note exactly which figure it wants, and for which period.
2. Read the headers, units and key. This is where most traps sit. A table headed “£000s” or a column in pence when the answers are in pounds is deliberate.
3. Find only the cells you need. Most tables hold far more data than any one question uses.
4. Check whether a total row is a total or a category. Using the overall total when the question asked about one department is a very common error.
5. Estimate before calculating. If the options are well spread, an estimate may be enough.
6. Sense check. A fall should give a negative change. A share should be under 100%.

Worked example 1: a table

A company records oil production and the average price per barrel.

Month	Barrels produced	Average price per barrel
April	18,000	$76
May	13,000	$89

Question: By what percentage did the value of oil produced change from April to May, to two decimal places?

1. Value in April: 18,000 × $76 = $1,368,000.
2. Value in May: 13,000 × $89 = $1,157,000.
3. Difference: $1,157,000 minus $1,368,000 is a fall of $211,000.
4. Percentage change: 211,000 ÷ 1,368,000 × 100 = 15.42%.

Answer: the value fell by 15.42%.

The trap here is working with barrels alone. Production fell by 5,000 barrels, about 27.8%, but the higher price softened the fall in value. Always check what the question means by “value”. For the method behind step 4, see our guide on how to calculate percentage decrease.

Worked example 2: a line graph

A line graph shows a firm’s quarterly revenue. The point for January to March sits at £30,000 and the point for April to June sits at £25,000.

Question: What was the average monthly revenue from January to June, to the nearest pound?

1. Read the two values you need: £30,000 and £25,000. Ignore the rest of the year.
2. Add them: £30,000 + £25,000 = £55,000.
3. Divide by the number of months, not quarters: January to June is 6 months, so £55,000 ÷ 6 = £9,166.67.

Answer: £9,167.

A quick estimate confirms it: £60,000 ÷ 6 would be £10,000, so the answer should be a little under that. Dividing by 2 for two quarters instead of 6 months is the most likely mistake, and it would give £27,500.

Worked example 3: projecting forward

Some questions ask you to extend data beyond what is shown.

Question: A chart shows revenue per employee of £34,500 in Year 3, and a note says it is forecast to rise by £500 each year. What is the ratio of Year 4 to Year 6, as a decimal to two places?

1. Year 4 = £34,500 + £500 = £35,000.
2. Year 6 = £35,000 + £500 + £500 = £36,000.
3. Ratio: 35,000 ÷ 36,000 = 0.9722…, which is 0.97.

The key detail is in the note, not the chart. Questions that combine the two are common, so read every line around the data.

Common traps

• The wrong period: using last quarter when the question asked about last year.
• Mixed units: thousands against millions, pence against pounds, or percentages against absolute numbers.
• The wrong base: a percentage change is always calculated from the original value.
• Reading a chart too precisely: use a chart for direction and a table for exact figures. Where only a chart is given, the answer options are usually far enough apart for a careful reading.

How to get better at data interpretation

Practise reading real tables and charts: company reports, news graphics and household bills are all useful. Work on speed with percentages, averages and ratios until the arithmetic is automatic. Then practise full questions against the clock. Our numerical reasoning test examples cover more question styles.

When you are ready to test yourself, take a free numerical reasoning test and review the worked solution for every question you miss.