Collecting and Representing DataAQA GCSE Maths: Revision notes

Section 1

What Types of Data Can We Collect?

Before collecting data, you must understand the vocabulary used to describe it:

Primary data: data you collect yourself, first-hand
Secondary data: data collected by someone else, that you then use
Discrete data: data that can only take specific, separate values (e.g. number of siblings)
Continuous data: data that can take any value within a range (e.g. height, time)

Key termsprimary datasecondary datadiscrete datacontinuous data

Example

The number of pets a student owns is discrete data; the exact time it takes to run 100 m is continuous data.

Section 2

How Do We Choose an Appropriate Graphical Representation?

Once data is collected, it can be interpreted, analysed and compared across different data sets using a graphical representation that suits the type of data — discrete, continuous or grouped. Choosing the right diagram for the data is a key skill: categorical data suits different charts to continuous numerical data, for example.

Key termsgraphical representation

Section 3

How Do We Represent Categorical and Discrete Data?

Different diagrams suit different types of data:

Diagram	Best suited to
Frequency table	Any data, as a first step
Bar chart	Categorical data
Pie chart	Categorical data (proportions of a whole)
Pictogram	Categorical data
Vertical line chart	Ungrouped discrete numerical data
Tables and line graphs	Time series data

You should be able to interpret and construct each of these correctly, and to justify why a chosen diagram suits a particular data set.

Key termsbar chartpie charttime series

Common mistake

Using a bar chart for continuous data (with gaps between bars) instead of a histogram or line graph is a common error — categorical data uses gaps, continuous data usually does not.

Must Know

Know the difference between primary and secondary data, and between discrete and continuous data
Choose a graphical representation that suits the type of data being shown (categorical, discrete or continuous)
Use bar charts, pie charts and pictograms for categorical data
Use vertical line charts for ungrouped discrete numerical data
Use tables and line graphs for time series data
Always be ready to justify why a particular diagram is suitable for a given data set

That's the notes covered.

Carry on to the next subtopic.