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  Data Picking

Information may be collected by people for their work.
For example, journalists need information to write articles and teachers need classwork and homework marks in order to write reports for parents.

Data
Items of information are called data. If you are asked about your favourite colour, your answer is an item of data. If many people are asked, the data will be collected in a tally table and charts may be drawn to show the information about their favourite colours.

Bar Chart

From this simple bar chart it can be seen that 2 people chose red, 3 blue and 1 yellow. Bar charts are very useful for showing data that is individual (e.g. pets, favourite lesson).

Pie Charts
Data can be charted as segments of a circle. This type of chart is called a pie chart.
If there are 6 people and each one has an equal share of the circle, each segment would be 60º as 360º ÷ 6 = 60º.

Pie Chart
Yellow 60º
Red 120º
Blue 180º

Pie charts are popular because they are useful for comparing data quickly.

Pie Charts for Grouped Data
Information can be confusing when there are many ways to answer a question.

If you were asked about your pocket money, your item of data could be one of many possible answers.

Data is often grouped to avoid the confusion caused by many answers.

For pocket money, the data could be placed in groups such as:

  • 'less than £2'
  • '£2 and less than £4'
  • '£4 and less than £6'
  • '£6 or more'
The whole circle is then divided by the number of people asked, the total frequency. Each group frequency is multiplied by this number to find the correct share of the circle.

Pie Chart

The total frequency is 10 people. Each person is represented in the pie chart by (360º ÷ 10) = 36º

Pocket Money Frequency Angle in the circle
Less than £2 1 36º
£2 and less than £4 4 4 x 36 = 144º
£4 and less than £6 3 3 x 36 = 108º
£6 or more 2 2 x 36 = 72º
Total 10 360º

Histograms for Grouped Data
A histogram is commonly used to represent grouped data. It looks like a bar chart, but there are several differences. The sections of the chart join and the axes have scales. In this example all the groups have the same width.

Pocket Money Frequency
Less than £2 1
£2 and less than £4 4
£4 and less than £6 3
£6 or more 2
Total 10

Frequency Chart

Estimates of the number of people receiving a particular amount can be made from the chart.

Line graphs
These are used instead of bar charts when one item of data is connected with the next item. This happens with data about a hospital patient's temperature. A line graph is used to show how the temperature changes through the day.

Time Temperature (º C)
0900 33
1200 34
1500 35
1800 34
2100 35

Line Graph

When the data is grouped the points are shown at the centre of the group to show that it represents the whole range of values.


Shoe size Shoe size
Less than 2 3
2 but less than 4 2
4 but less than 6 4
6 but less than 8 1
Total 10

Line Graph

Scatter Diagrams


These show two items of data for each person. The shape of the scatter diagrams indicates whether there is a relationship between the two categories of information.


Student
Maths mark(10)
English mark (10)
A
1
8
B
1
6
C
3
5
D
4
3
E
6
3
F
6
5
G
7
1

Scatter Diagram

Each point is plotted using the Maths and English marks as co-ordinates. The general direction of the points shows that, for this group of students, those that do well in English do poorly in Maths. This is called negative correlation between English and Maths marks.

 Correlation

The other possibilities are: positive correlation, if those that did well in English also did well in Maths; and no correlation, if the mark in English had no connection with the Maths mark.

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