Collecting and Representing Data Notes

AQA GCSE Maths: Revision notes

Key facts

Primary data is collected first-hand; secondary data was collected by someone else.
Discrete data takes separate values; continuous data can take any value in a range.
Choose a diagram that suits the type of data, and be ready to justify it.
Bar charts, pie charts and pictograms suit categorical data; vertical line charts suit ungrouped discrete data.
Line graphs suit time series data.

Types of data

Data is primary or secondary depending on who collected it, and discrete or continuous depending on the values it can take.

Before collecting data, know the vocabulary.

Primary data is collected first-hand. Secondary data was collected by someone else and you then use it.

Discrete data has specific, separate values. Continuous data can take any value in a range. The number of pets is discrete; the exact time to run 100 m is continuous.

Number of siblings (illustrative values): discrete data takes separate values, so the bars are separate.

Primary data Secondary data Discrete data Continuous data Meaning Collected first-hand Collected by someone else Separate values Any value in a range Example Your own survey Published census figures Number of siblings Height or time

	Primary data	Secondary data	Discrete data	Continuous data
Meaning	Collected first-hand	Collected by someone else	Separate values	Any value in a range
Example	Your own survey	Published census figures	Number of siblings	Height or time

Primary data

Meaning:: Collected first-hand
Example:: Your own survey

Secondary data

Meaning:: Collected by someone else
Example:: Published census figures

Discrete data

Meaning:: Separate values
Example:: Number of siblings

Continuous data

Meaning:: Any value in a range
Example:: Height or time

Which of these is continuous data?

Choosing a representation

Identify the type of data first: it decides which diagrams are suitable.

Data can be interpreted, analysed and compared across data sets using a graphical representation that suits the data: discrete, continuous or grouped.

Categorical data suits different charts to continuous numerical data, so choosing the diagram is a key skill.

1
Identify the data type
categorical, discrete or continuous
2
Pick a suitable diagram
match it to the data type
3
Construct it
label axes, scales and title
4
Justify
say why the diagram suits the data

Choosing a diagram

What should you do first when choosing a graphical representation?

Categorical and discrete data

Bar charts, pie charts and pictograms show categories; vertical line charts show discrete numbers; line graphs show time series.

A frequency table is a first step for any data. Know how to interpret and construct each diagram, and to justify why it suits the data.

A bar chart shows categories with gaps between bars; a pie chart shows proportions of a whole. A time series is data collected at successive times, shown on a line graph.

Favourite pet (illustrative values): a bar chart for categorical data, with gaps between the bars.

Categorical data

Bar chart
Pie chart
Pictogram

Ungrouped discrete data

Vertical line chart
Frequency table

Time series data

Line graph
Table

Which diagram is best for showing temperature recorded every hour through a day (time series data)?

Try an exam question

The time taken to run 100 m is recorded for each member of a team. State whether this data is discrete or continuous, with a reason. Hourly temperatures are recorded through a day. Name a suitable diagram and give a reason.

[4 marks]

That's the notes covered.

Carry on to the next subtopic.