Tables, charts and graphs in economics: WASSCE Economics

"Rice prices are going up" is an opinion until someone shows the figures. Economists turn numbers into tables, charts and graphs so that patterns can be seen at a glance. WASSCE asks you to draw and read every one of them.

Learning objectives

By the end of this lesson you should be able to:

present economic data in tables
draw and read bar charts, pie charts, line graphs and histograms
choose the right kind of chart for a set of data

Why economists use tools

Economists work with large amounts of information: prices, output, incomes, population. Tables, charts and graphs make this information easier to read, compare and explain. WAEC expects you to construct these and to interpret them.

Tables

A table arranges data in rows and columns. A good table has:

a clear title
headings for every column, with units (bags, NLe, %)
the source of the data where it is known

Worked example

Rice sold by a shop in one week

Day	Bags sold
Monday	12
Tuesday	8
Wednesday	10
Thursday	6
Friday	14
Total	50

From the table we can see at a glance that Friday was the busiest day and Thursday the quietest.

Bar charts

A bar chart shows quantities as bars of equal width; the height (or length) of each bar shows the value.

Use it to compare separate items or periods, such as sales on different days.
Leave equal gaps between the bars.
Label both axes and start the value axis at zero.

Bar chart of bags of rice sold each weekday: Monday 12, Tuesday 8, Wednesday 10, Thursday 6, Friday 14

Figure 1. Bar chart of the rice sales in the table above. WASSCE Tutor diagram.

A component (subdivided) bar chart splits each bar into parts, for example a family's spending each year divided into food, rent and transport.

Pie charts

A pie chart is a circle divided into sectors. Each sector shows a share of the whole.

Because a full circle is 360°, each item's angle is:

\text{angle} = \dfrac{\text{value of the item}}{\text{total}} \times 360^\circ

\begin{aligned}&\text{angle} \\ &= \dfrac{\text{value of the item}}{\text{total}} \times 360^\circ\end{aligned}

Worked example

A household spends NLe 600 a month:

Item	Spending (NLe)	Angle
Food	300	$\dfrac{300}{600} \times 360^\circ = 180^\circ$
Rent	150	$\dfrac{150}{600} \times 360^\circ = 90^\circ$
Transport	90	$\dfrac{90}{600} \times 360^\circ = 54^\circ$
School fees	60	$\dfrac{60}{600} \times 360^\circ = 36^\circ$
Total	600	360°

Always check that your angles add up to 360°.

Pie chart of a household's NLe 600 monthly spending: food 180 degrees, rent 90 degrees, transport 54 degrees and school fees 36 degrees

Figure 2. Pie chart of the household spending in the table. WASSCE Tutor diagram.

Common mistake

Students often draw a pie chart without first working out the angles, or forget to check the total. Show your working in a table like the one above: examiners award marks for the calculation as well as the drawing.

Line graphs

A line graph joins plotted points with a line. It is best for showing how something changes over time, such as the price of rice month by month.

Time goes on the horizontal (x) axis.
The variable being measured goes on the vertical (y) axis.
A rising line shows an increase; a falling line shows a decrease; a steep line shows fast change.

Worked example

Price of a 50 kg bag of rice (illustrative figures, NLe)

Month	Price (NLe)
January	650
February	660
March	700
April	720
May	760
June	750

Line graph of the price of a bag of rice rising from NLe 650 in January to NLe 760 in May, then dipping to NLe 750 in June

Figure 3. Line graph of the rice prices in the table. WASSCE Tutor diagram.

The line rises steeply from February to March (+40) and from April to May (+40), and falls slightly in June. The vertical axis starts at NLe 600, shown by the break mark (≈) near the origin, so that the changes are easy to see.

Graphs of relationships

Economists also use graphs to show how two variables are related. A demand curve, for example, plots price against quantity demanded. When one variable rises as the other falls, the line slopes downwards (a negative or inverse relationship). When both rise together, it slopes upwards (a positive or direct relationship).

Histograms

A histogram shows a frequency distribution of grouped, continuous data, such as incomes or ages in classes. It looks like a bar chart, but:

the bars touch, because one class runs straight into the next
the area of each bar represents the frequency (with equal class widths, the height does too)

Worked example

Daily earnings of 40 market traders

Earnings (NLe)	0–49	50–99	100–149	150–199	200–249
Number of traders	4	9	14	8	5

Histogram of traders' daily earnings with touching bars: 4 traders earn NLe 0 to 49, 9 earn 50 to 99, 14 earn 100 to 149, 8 earn 150 to 199 and 5 earn 200 to 249

Figure 4. Histogram of the traders' earnings. WASSCE Tutor diagram.

The tallest bar shows the modal class: NLe 100–149, earned by 14 traders.

Choosing the right tool

You want to show…	Use
Exact figures for reference	A table
A comparison between separate items	A bar chart
Shares of a total	A pie chart (or a component bar chart)
A change over time	A line graph
How grouped, continuous data is spread	A histogram
The relationship between two variables	A graph with both variables on the axes

Key points

Every table, chart and graph needs a title, labelled axes or headings and units.
Pie chart angle = value ÷ total × 360°.
Use bar charts to compare, pie charts for shares, line graphs for trends and histograms (touching bars) for grouped frequency data.

WASSCE examination focus

WAEC tests this

Data questions are common. You may be asked to construct a pie chart or bar chart from a table, or to read a graph and explain a trend. Use a ruler and protractor, label everything, give a title and show calculations. When interpreting, quote figures from the data ("sales rose from 6 bags on Thursday to 14 on Friday") rather than describing in general terms.

Quick check

A firm's total costs are NLe 2,000, of which wages are NLe 500. What angle would wages take in a pie chart?
Which chart is best for showing how the price of fuel changed over twelve months?
What does a downward-sloping line on a graph tell you about two variables?

Answers: 1. $\dfrac{500}{2000} \times 360^\circ = 90^\circ$ . 2. A line graph. 3. They have an inverse relationship: as one rises, the other falls.

Tables, charts and graphs in economics

Learning objectives

Why economists use tools

Tables

Bar charts

Pie charts

Line graphs

Graphs of relationships

Histograms

Choosing the right tool

Key points

WASSCE examination focus

Quick check

Keep going with tools of economic analysis

More lessons in Tools of Economic Analysis