OxfordAQA AS and A-level Economics: Graphs and interpreting information (9640)

This guide covers quantitative skills QS4 and QS9 in section 3.5 of the OxfordAQA International AS and A-level Economics (9640) specification, version 1.2. The specification says these skills could be assessed in any of the assessments. Sections 3.1 and 3.2 are International AS content and sections 3.3 and 3.4 are the extra International A2 content, and the specification gives no extra A2 requirement for either skill. All the countries, firms and figures below are made up for illustration. Use the OxfordAQA Economics hub and the printable checklist to track progress, and try the free diagnostics to find weak spots.

What the two skills say

Skill	Specification wording	What you do in practice
QS4	construct and interpret a range of standard graphical forms	Draw and read line graphs, bar charts, pie charts, scatter graphs and economics diagrams
QS9	interpret, apply and analyse information in written, graphical and numerical forms	Pull evidence from text, charts and tables, use it, and judge how far it supports a conclusion

The specification does not list which graphical forms count. This guide therefore teaches the forms that economics data usually arrive in, and it treats supply and demand diagrams as graphs with axes, intercepts and gradients. Skills such as percentages, index numbers and elasticity are separate items in the same section, so see the ratios and percentages guide and the demand and elasticity guide. The revision notes condense this page and the practice set tests it.

Choosing the right graphical form

Form	Best for	Watch for
Line graph	Change over time, such as a growth rate each year	Time on the horizontal axis; do not join points that are not a series
Bar or column chart	Comparing separate categories or a few dates	Bars must start at zero
Compound (stacked) bar	Total and parts together	Only the bottom part is easy to compare across bars
Pie chart	Shares of one total at one moment	Poor for comparing more than one total
Scatter graph	Whether two variables move together	Pattern is not proof of cause
Economics diagram	Price, quantity, cost or revenue relationships	Label axes, curves and equilibrium

Constructing a graph: the checklist

1. Decide the form from the question being asked.
2. Put the independent or time variable on the horizontal axis. Economics diagrams are the exception: price goes on the vertical axis even though price is usually the cause.
3. Choose an even scale, so equal distances represent equal amounts, and say whether the axis starts at zero.
4. Label both axes with the variable and the unit, for example “Real GDP growth (% per year)”.
5. Plot every point, then join them only if the data form a continuous series.
6. Add a title and, for real data, a source. Label each line or curve directly.

Worked example 1: a time series

Country A (illustrative) has real GDP of 200 billion units in 2015. Its annual real growth rates are: 2016: 3.0%, 2017: 3.5%, 2018: 2.0%, 2019: -1.5%, 2020: -4.0%, 2021: 2.5%, 2022: 4.0%.

Each year’s level is the previous level multiplied by (1 + growth rate):

2016: 200 x 1.030 = 206.00
2017: 206.00 x 1.035 = 213.21
2018: 213.21 x 1.020 = 217.47
2019: 217.47 x 0.985 = 214.21
2020: 214.21 x 0.960 = 205.64
2021: 205.64 x 1.025 = 210.78
2022: 210.78 x 1.040 = 219.22

A line graph of the growth rate dips below the horizontal axis in 2019 and 2020. A line graph of the level peaks in 2018 and troughs in 2020. In 2021 the growth rate is positive, yet the level (210.78) is still below the 2018 peak (217.47). Output only passes its 2018 peak in 2022. The interpretation rule is that a growth rate describes the slope of the level graph, not its height. Output can be recovering and still be lower than before the downturn.

Worked example 2: a pie chart

Country B (illustrative) spends 80 billion units. Health 24, education 16, welfare 20, defence 8, debt interest 6, other 6.

Angle = (item / total) x 360
Health:    24/80 x 360 = 108 degrees  (30%)
Education: 16/80 x 360 =  72 degrees  (20%)
Welfare:   20/80 x 360 =  90 degrees  (25%)
Defence:    8/80 x 360 =  36 degrees  (10%)
Debt:       6/80 x 360 =  27 degrees  (7.5%)
Other:      6/80 x 360 =  27 degrees  (7.5%)

The angles sum to 360 degrees, which is the check. A pie shows shares only. It cannot show that total spending rose, so a claim such as “health spending grew” needs a second year’s total.

Worked example 3: a compound bar chart

Country E (illustrative) has exports of 100 in 2019 (goods 60, services 40) and 120 in 2024 (goods 66, services 54).

	2019	2024	Change
Goods	60	66	+10%
Services	40	54	+35%
Total	100	120	+20%
Services share	40%	45%	+5 percentage points

Services grew faster than goods (54/40 = 1.35 against 66/60 = 1.10), so their share of the total rose. A 100% stacked bar would show the shares but hide that the total grew by a fifth. Choose the version that matches the point you want to make.

Worked example 4: a scatter graph

Town C (illustrative) records household income (thousand units a year) and monthly spending on restaurant meals (units) for eight households.

Income	20	25	30	35	40	45	50	60
Spending	40	50	55	70	70	85	90	110

The mean income is 38.1 and the mean spending is 71.25, so the cloud of points sits around (38.1, 71.25). Sketch a trend line by eye so that it runs near that mean point with the points scattered evenly on both sides. Suppose it passes through (20, 40) and (60, 108). Its gradient is (108 - 40)/(60 - 20) = 68/40 = 1.7. Read this as: on this sample, each extra thousand units of income goes with about 1.7 more units spent a month.

Three cautions apply. The relationship is positive, but income may not be the only cause. A prediction for an income of 70 uses the line outside the data range, so it is less reliable than one for 42. Eight households is a small sample, so one unusual household could shift the line.

Economics diagrams as graphs

Suppose demand is Qd = 110 - 4P and supply is Qs = 6P - 30, with price (P) in units and quantity (Q) in thousands.

• Equilibrium: 120 - 4P = 10P - 20, so 140 = 10P, P = 14 and Q = 54.
• Demand cuts the price axis at 27.5 (set Q to zero) and the quantity axis at 110 (set P to zero). Supply cuts the price axis at 5.
• Because price is on the vertical axis, rewrite demand as P = 27.5 - 0.25Q. The gradient is -0.25, the reciprocal of the coefficient on price in the quantity equation, with the same sign.
• Consumer expenditure is the rectangle with width 54 and height 14, so 756.

A per-unit tax of 5 on suppliers shifts supply up by 5: Qs = 6(P - 5) - 30 = 6P - 60. Then 110 - 4P = 6P - 60 gives P = 17 and Q = 42. Consumers pay 3 more. Producers receive 17 - 5 = 12, which is 2 less. Tax revenue is 5 x 42 = 210. Consumers bear 3/5 of the tax, or 60%, because demand is less responsive to price than supply is at the starting equilibrium (price elasticity of demand about 1.04 against about 1.56 for supply).

Reading graphs critically

• Truncated axis. A firm’s sales rise from 480 to 504, which is 5%. If the axis starts at 470, the bars are 10 and 34 units tall, so the second looks 3.4 times the first. Check where an axis starts.
• Dual axes. Two lines on different scales can be made to cross or run together by changing the scales. Compare the actual values.
• Levels and rates. Inflation falling from 6% to 3% means prices still rise, only more slowly.
• Percentage points. An unemployment rate moving from 6.0% to 7.5% is a rise of 1.5 percentage points, or 25% in relative terms.
• Index numbers. An index shows change from a base year, not the amount.

Interpreting written information

Written extracts in data-response questions hold claims, figures and context. Work through them in four steps.

1. Extract. Underline the figures and who said them.
2. Quantify. Turn the figures into a percentage, ratio or gradient.
3. Connect. Link the result to a concept, such as elasticity or opportunity cost.
4. Judge. Say what the evidence cannot show.

Worked example 5. An extract from Town D (illustrative) says: “After the average café price rose 12%, customer numbers fell 6%.” Price elasticity of demand is -6/12 = -0.5, so demand is inelastic over this range. Revenue is 1.12 x 0.94 = 1.0528, a rise of 5.3%. The café owners gained revenue, but this does not say profit rose, because the extract gives no costs. It also does not say the price rise alone caused the fall in customers.

Evaluation chains

A strong data answer follows a chain: the figure, what it means, why it matters, and a limit. For example: services exports grew 35% (figure), so the economy is becoming more service-based (meaning), which may make it less exposed to goods price swings (why it matters), although two years of data cannot show a trend (limit).

Common errors

• Reading a falling growth rate as a falling level.
• Giving percentage-point and percentage changes the same name.
• Starting a bar chart axis above zero without saying so.
• Joining scatter points with a line.
• Quoting a figure without the unit or year.
• Stating a cause from a correlation alone.

Official syllabus

OxfordAQA International AS and A-level Economics (9640) specification, version 1.2, section 3.5 Quantitative skills, items QS4 and QS9. Published by OxfordAQA.