Graphics

Quiz 2 material for ENSC 105W

• Importance of graphics

  • A typical reader will look at

    • The title

    • The abstract

    • The introduction

    • The figures, graphs, charts

    • Skim other sections based on need

• What makes a good graphic

  • You need to properly introduce the graphic

    • then having it explained and introduced the reader will under stand what the graphic means and the importance

• Types of graphics

  • A lot can be considered graphics

    • To convey a message by means of drawing lines

      • text
      • pictures
      • diagrams

• Number can lie

  • For example

    • when looking at stats you can have 4 different data sets that average out to be the same but give out different values
    • 

Use Tufte’s measures to optimize graphics

• Tufte’s measures

  • Maximize data-ink ratio

    • data-ink ratio = data ink/total ink used in graphic

    • Keep it simple

  • maximize data density

    • data density = # entries in data matrix/ area of data graphic

    • If comparing graph, merge

  • Avoid lie factors

    • lie factor = size of effect shown in graphic/size of effect in data

    • avoid changing the graph to lie

recognize how to select the most appropriate graph type

• Whats wrong with this graph

  • 

    • Colours

    • using the wrong type of graph it should be a bar graph (by month)

• types of graphics

  • 

  • Bar graphs

    • Grouped bar:

      • 
      • Compare relationships

    • Stacked bar:

      • 
      • compare parts to whole

    • Deviation bar:

      • 
      • difference from an expected value

    • Sliding bar:

      • 
      • how groups split according to some characteristic

  • Scatter plots

    • Shows correlations between two uncontrolled sets of data

    • 

  • Pie charts

    • comparing parts to a whole

    • good for small number of segments

  • Colour

    • determine whether document will be reproduced in colour or black and white

    • keep in mind that people will often print in black and white

      • avoid reference like “the red line shows”
      • pay attention to contrast issues

    • general rule is that a diagram should be understandable reading a photocopied photocopy

Incorporate graphics into text and oral presentations

• Ensuring graphical integrity

  • # of variables changing in graphic = # of variables changing in data

  • Use clear labels

  • show change in data, not change in designs variation

  • Show standardized units for money

  • Demonstrate cause and effect

  • Use the correct type of graphic

• Graphics in oral presentations

  • Think PGP (particular, general, particular)

    • introduced figure
    • point to a particular data point
    • describe the overall trend
    • reinforces by explaining

Case study of Challenger

• The disaster

  • the shuttle relied on temperature sensitive o rings

    • many people did not see the damage and tempeture correlation because of the figure