Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Thomson Learning 2004 Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Cengage Chapter 4: Representing Data

Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Thomson Learning 2004 Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Cengage Objectives Construct bar charts Construct pie charts Construct pictograms Construct histograms Have basis for choice of graph

Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Thomson Learning 2004 Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Cengage Simple Bar Chart Easy to understand Useful for categorical data Useful for reporting survey results All bars same width Length represents frequency Eye Colour

Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Thomson Learning 2004 Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Cengage Stacked Bar Chart For more complex situations Contain more data But may complicate the picture too much Can be just stacked, or percentage Percentage may be easier to understand

Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Thomson Learning 2004 Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Cengage Pie Charts Good for categorical data Good for reporting survey results Danger of misunderstanding or confusion if too many segments Pull out a segment for emphasis Easy to construct from Excel

Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Thomson Learning 2004 Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Cengage More Pie Charts Can go to 3D for effects But may confuse audience Can link 2 or more together Gender balance in Britain

Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Thomson Learning 2004 Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Cengage Pictograms Good at attracting attention Make picture relevant to the topic Can be misleading Many different ways of presenting results

Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Thomson Learning 2004 Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Cengage Pictograms (2) To show a doubling from last years production, this is last year If we double the height of the picture If we double to volume of the picture

Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Thomson Learning 2004 Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Cengage Histograms Key point that here it is the area which represents frequency Term is often misused and a bar-chart has been drawn Works for discrete data Can go on to get frequency polygons Link to development of statistical theory and probability density functions

Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Thomson Learning 2004 Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Cengage Histograms (2) Number of Children Number of Families Discrete data, so all bars are same width Some would not call this a histogram

Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Thomson Learning 2004 Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Cengage Histograms (3) Income Group Number of People £5,000 but under £10,00050 £10,000 but under £15,00080 £15,000 but under £20, £20,000 but under £30,00080 £30,000 but under £50,00040 £50,000 but under £100, Height With grouped dataPick a width as standard and relate others to it. Now divide frequency by relative width to get height

Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Thomson Learning 2004 Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Cengage Histograms (4) Now plot using a linear scale on X-axis

Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Thomson Learning 2004 Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Cengage Frequency Polygon By joining up the mid-points of the histogram blocks we get a frequency polygon This allows us to assess skewness in the distribution

Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Thomson Learning 2004 Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Cengage Using Excel Excel can quickly and easily construct statistical graphs Excel does not do histograms You have to decide which are appropriate Colour graphics may look good on screen, but often fail when printed out in black and white

Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Thomson Learning 2004 Jon Curwin and Roger Slater, QUANTITATIVE METHODS: A SHORT COURSE ISBN © Cengage Conclusions Statistical charts are about communication When assessing a chart you need to ask if it succeeds in telling you what is going on. There are few “right” answers in terms of which diagram to use, but some may be viewed as “more appropriate” than others