Topic 16 – Graphs and Charts (IGCSE 0417)
Learning Objective (AO2)
Students must be able to select the most appropriate graph or chart type for a given data set, justify the choice using the exact exam command words (e.g. select, justify, explain, describe, comment), and produce a correctly labelled and edited visualisation.
Why Choosing the Right Graph Matters
- Enables the audience to spot trends, patterns and relationships quickly.
- Allows accurate comparison of values.
- Communicates the intended message without distortion.
- Supports informed decision‑making based on the data.
Purpose Categories (as used in the syllabus)
- Compare – show differences between categories or groups.
- Trend – show how a quantity changes over a continuous interval (usually time).
- Proportion – illustrate parts of a whole (percentages).
- Relationship – explore correlation or lack of correlation between two quantitative variables.
Command‑Word Bank (AO2)
Use the exact wording in the exam question when writing your justification. Typical command words are:
- select – “I have selected a … because …”
- justify – “I justify the use of a … because …”
- explain – “I explain that a … is appropriate because …”
- describe – “I describe the data as … and therefore a … is suitable.”
- comment – “I comment that the … best shows …”
Common Graph and Chart Types
| Graph / Chart Type |
Best For (Purpose) |
Data Type Required |
Typical IGCSE Example |
| Bar Chart |
Compare individual categories side‑by‑side |
Nominal or ordinal (categorical) data |
Number of books sold per genre in a month |
| Column Chart |
Compare categories over a time period (vertical orientation) |
Nominal data with a time dimension (e.g. months, quarters) |
Quarterly revenue for each region |
| Line Graph |
Show a trend or change over a continuous interval |
Continuous quantitative data (usually time) |
Average monthly temperature for a year |
| Pie Chart |
Display parts of a whole as percentages |
Percentages / fractions that add up to 100 % |
Market‑share of five companies |
| Scatter Plot |
Examine correlation (or lack of) between two quantitative variables |
Two continuous quantitative variables |
Height vs. weight of a class of students |
| Histogram |
Show the frequency distribution of a single quantitative variable |
Continuous quantitative data grouped into equal intervals |
Distribution of test scores in 10‑point bands |
| Stacked Bar / Column Chart |
Compare totals while also showing the contribution of sub‑categories |
Nominal data with sub‑categories (e.g. product line + region) |
Sales by product line broken down by region |
Key Distinction: Bar Chart vs. Histogram
- Bar chart – used for categorical data; bars are separated.
- Histogram – used for continuous data; bars touch to show the continuity of intervals.
AO2 Checklist – Selecting the Most Appropriate Graph
- Identify the purpose – compare, trend, proportion, or relationship?
- Determine the data type(s) – categorical, ordinal, continuous, percentages, or a mix.
- Count the variables:
- One variable → bar, column, pie, histogram.
- Two variables → line, scatter, stacked bar/column (if one variable is categorical).
- More than two → stacked charts, multiple series, or a combination chart.
- Check units and scales – do the series have different units or vastly different magnitudes? If yes, a secondary vertical axis may be required.
- Consider the audience – choose a familiar, non‑decorative chart type.
- Ensure the chart will not distort the data – start the axis at zero unless doing so would hide important variation; avoid 3‑D effects, unnecessary shading or “exploded” pies.
- Write a justification using the command‑word bank (e.g. “I have selected a line graph because the data are continuous monthly sales figures and a line graph best shows the trend over time”).
Decision Tree for a Secondary Axis (AO2)
- Do you have two data series on the same chart?
- No → use a single axis.
- Yes → go to 2.
- Do the series have different units (e.g. £ vs. units sold) or vastly different scales?
- No → keep a single axis.
- Yes → add a secondary vertical axis, label it clearly with its own unit.
Labelling & Editing Checklist (AO2 – Creation & Editing)
- Title – concise, describes exactly what the chart shows.
- Axis labels – variable name + unit (e.g. “Revenue (£)”).
- Scale & intervals – start at zero where appropriate; use equal intervals; label every tick.
- Legend – required when more than one data series or colour is used.
- Data labels / markers – optional but useful for exact values in bar/column charts.
- Colours & line styles – high‑contrast, colour‑blind‑friendly palette; keep styles consistent.
- Secondary axis – only when needed; label with its own unit.
- Number formatting –
- Currency: £, $ or € with two decimal places (e.g. £12.50).
- Percentages: show % sign with one decimal place unless the data require more (e.g. 23.5 %).
- Plain numbers: use the number of decimal places given in the source; avoid unnecessary trailing zeros.
- Source (if required) – give a brief citation beneath the chart.
Evaluating the Effectiveness of a Graph (AO3)
After creating the visualisation, ask yourself:
- Is the scale appropriate, or does it exaggerate/understate differences?
- Does the chart answer the original purpose (compare, trend, proportion, relationship)?
- Are all labels clear, legible and correctly placed?
- Is the colour scheme accessible (no reliance on red‑green only)?
- Are any 3‑D effects, unnecessary shadows or decorative elements present that could mislead?
- Is any part of the data omitted or presented in a way that could be misleading?
- Would another chart type convey the information more clearly?
e‑Safety & Data Protection (AO1)
When using real‑world data:
- Remove or anonymise personal identifiers (e.g. replace student names with ID numbers).
- Only display data that are publicly available or for which you have explicit permission.
- Store the original data securely and cite the source.
Software‑Tool Independence (AO2)
The syllabus does not prescribe a particular program. Any spreadsheet or data‑visualisation software that can produce the chart types listed above is acceptable (e.g. Microsoft Excel, Google Sheets, LibreOffice Calc). Teachers should avoid brand‑specific shortcuts in the notes and focus on the *principles* of inserting, editing and formatting a chart.
Practice Exercise
For each data set, select the most appropriate graph or chart type and write a one‑sentence justification that uses an exam command word.
- Number of books sold by genre (Fiction, Non‑fiction, Mystery, Science, Biography).
Suggested answer: Bar chart – I have selected a bar chart because the data are categorical and the aim is to compare the sales of each genre.
- Average daily temperature recorded over a 12‑month period.
Suggested answer: Line graph – I have selected a line graph because the data are continuous monthly values and a line graph best shows the temperature trend over the year.
- Proportion of budget allocated to marketing, research, operations, and administration.
Suggested answer: Pie chart – I have selected a pie chart because the data represent parts of a whole (100 %) and a pie chart displays the relative percentages clearly.
- Relationship between hours studied and exam score for a group of students.
Suggested answer: Scatter plot – I have selected a scatter plot because both variables are quantitative and a scatter plot reveals any correlation between study time and marks.
- Frequency of test scores grouped in intervals of 10 points (0‑10, 11‑20, …, 91‑100).
Suggested answer: Histogram – I have selected a histogram because the data are continuous scores grouped into equal intervals, and a histogram shows the distribution of frequencies.