A frequency diagram can be used as another way of representing data. The most well known frequency diagram is a bar chart. We can represent both qualitative and quantitive data with one (for more information about different types of data http://cribbd.com/learn/maths/data-handling/classify-and-know-the-difference-between-various-types-of-data)

Qualitative Data Example:

In a survey, 200 students were asked to name the method of tranport they use to get to and from school. The results are shown in the table below

Method of transport Number of students
Bus 42
Train 28
Walking 33
Car 97

To construct the bar chart, we're going to label our x-axis with 'Method of transport', and our y-axis with 'Number of students' (frequency). Then plot it using the table above.

From the graph above we can clearly see that taking the car is the choice of most of the students on this particular survey.

In essense a bar chart is a chart where the height of the bars represent the frequency.

Quantitative Data Example:

For discrete data, our bar graph would be very similar to the one above, but now instead of something that cannot be represented by numbers ( like what mode transport is used). We will now use something that can, like the number of children per household.

For example: The table below shows that number of children per household in a sample of 50 households.

Number of Children Number of Households
0 2
1 7
2 12
3 21
4 5
5 2
6 1

So like before, we're going to plot the number of children on the x-axis and the frequency which in this case is the number of households on the y-axis

For continuous data, the data needs to be set up different before we represent it with a graph. The list below represents the heights of 25 students 

 

166, 154, 142, 147, 164, 173, 178, 156, 158, 171, 182, 165, 145, 150, 153, 149, 154, 143, 151, 164, 157, 149, 164, 141, 155

In order to effectively represent this data using a bar graph, we need to group the data. 

Height(cm) Number of students
140-149 7
150-159 9
160-169 5
170-179 3
180-189 1

As you can see, none of the groups that have been chosen overlap one another. 

 

 

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AQA Unit 1 March 2011 (H) - Page 12, Question 9

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