Frequency tables for Continuous Data Check HW Frequency tables for Continuous Data

1 5 7 2 6 Most Used App 3&4 Frequency Type of App App Frequency Twitter 2 Instagram 5 Snapchat 8 WhatsApp 10 Facebook 7 Most Used App 1 5 10 9 8 7 6 Frequency 7 5 4 3 2 1 Twitter Instagram Snapchat WhatsApp Facebook 2 3&4 Type of App 6

Why do bar charts have gaps? Discrete or Qualitative Data Bar Chart showing the number of pets each student in a Year 7 class owned This type of data has distinct values. Only particular values are possible. We use gaps to show each group is separate. Frequency What about for Continuous data? Number of pets owned

Frequency diagrams can be used to display grouped continuous data. For example, this frequency diagram shows the distribution of heights for a group of students: Frequency Height (cm) 5 10 15 20 25 30 35 150 155 160 165 170 175 180 185 Heights of students Equal class intervals THE Y-AXIS IS LIKE A LONG RULER!! THE NUMBERS CONTINUE AND SO DO THE NUMBERS WITHIN THE RANGE – A CONTINUOUS SCALE FREQUENCY DIAGRAMS OFTEN HAVE VERTICAL BARS Stress that the difference between this graph and a bar graph is that the bars are touching. Bar graphs can only be used to display qualitative data or discrete numerical data where as histograms are used to show continuous data. Strictly speaking, for a histogram we plot frequency density rather than frequency along the vertical axis. However, this is not make any difference to the graph when the class intervals are equal as in this example. This type of frequency diagram is often called a histogram.

Bar Charts vs Histograms The difference between this diagram and a bar chart is that the bars are touching. Bar charts can only be used to display qualitative data or discrete numerical data where as histograms are used to show continuous data Strictly speaking, for a histogram we plot frequency density rather than frequency along the vertical axis. However, this is not make any difference to the graph when the class intervals are equal as in this example.

Histograms Histograms are used to display grouped continuous data. The frequencies go on the vertical axis. The class intervals go on the horizontal axis. The class intervals should all be the same width. There are no gaps left between the bars, to show that the data is continuous. Teacher notes Stress that bar graphs can only be used to display qualitative data or discrete numerical data, whereas histograms are used to show continuous data. Strictly speaking, for a histogram, frequency density rather than frequency is plotted along the vertical axis. However, this does not make any difference to the graph when the class intervals are equal as in this example. For more on grouping data into class intervals, see the presentation Frequency tables. The highest and lowest possible values in each interval go at either end of the bar: 80 85 90 The axes should always be labelled.

L.O. To be able to draw a simple Histogram By the end of the lesson we will be able to: understand the difference between a bar chart and a histogram draw a good histogram get information from a histogram

Histogram of cycling data The cycling data we looked at yesterday can be displayed in the following frequency diagram: Frequency 85 5 10 15 20 25 30 90 95 100 105 110 Times in seconds What conclusions can you draw from the graph?

Drawing a Simple Histogram Title the chart Start the vertical axis from 0 and space out the numbers evenly Make sure bars are of equal width Make sure there are NO GAPS to show continuous data Use a pencil and ruler to draw the axes Label the axes Draw the bars

Classwork: Peer Assessment STP 8 Pg 311 Ex 15d No. 2 2 marks for each step (14) 1 mark for neatness (total 15) Comment: what was done well, what can be done better on the next diagram?