Unit 8: Presenting Data in Charts, Graphs and Tables

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Unit 8 Presenting Data in Charts, Graphs and
Tables
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Warm Up Questions Instructions

• Take five minutes now to try the Unit 8 warm up
  questions in your manual.
• Please do not compare answers with other
  participants.
• Your answers will not be collected or graded.
• We will review your answers at the end of the
  unit.

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What You Will Learn

• By the end of this unit you should be able to
• list the variables for analysing surveillance
  data
• identify the types of charts and graphs and when
  the use of each is appropriate

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Analysing Surveillance Data

• Person Who develops a disease (for example, by
  age group or sex)? Are the distributions changing
  over time?
• Place Where are cases occurring? Is the
  geographical distribution changing over time?
• Time Is the number of reported cases changing
  over time?

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Purpose of Displaying Data

• The purpose of developing clearly understandable
  tables, charts and graphs is to facilitate
• analysis of data
• interpretation of data
• effective, rapid communication on complex issues
  and situations

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Types of Variables

• Categorical variables refer to items that can be
  grouped into categories.
• Ordinal variables are those that have a natural
  order.
• Nominal variables represent discrete categories
  without a natural order.
• Dichotomous variables have only two categories
• Continuous variables are items that occur in
  numerical order.

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General Rules for Displaying Data

• Simpler is better.
• Graphs, tables and charts can be used together.
• Use clear descriptive titles and labels.
• Provide a narrative description of the
  highlights.
• Dont compare variables with different scales of
  magnitude.

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Graphs

• A diagram shown as a series of one or more
  points, lines, line segments, curves or areas
• Represents variation of a variable in comparison
  with that of one or more other variables

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Scale Line Graph

• Scale line graph represents frequency
  distributions over time
• Y-axis represents frequency.
• X-axis represents time.

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Example Scale Line Graph
Figure 8.1. Trends in HIV prevalence
among pregnant women in Country X, years 1 10
Year
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Specific Rules Scale Line Graphs

• Y-axis should be shorter than X-axis
• Start the Y-axis with zero
• Determine the range of values needed
• Select an interval size

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Bar Charts

• Uses differently coloured or patterned bars to
  represent different classes
• Y-axis represents frequency
• X-axis may represent time or different classes

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Example Bar Chart
Figure 8.2. Differences in HIV prevalence among
various high-risk groups, Country X, year 1.
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Specific Rules Bar Charts

• Arrange categories that define bars in a natural
  order (for example, age).
• If natural order does not exist, define
  categories by name, such as country, sex or
  marital status.
• Position the bars either vertically or
  horizontally.
• Make bars the same width.
• Length of bars should be proportional to the
  frequency of event.

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Clustered Bar Charts

• Bars can be presented as clusters of sub-groups
  in clustered bar charts.
• These are useful to compare values across
  categories.
• They are sometimes called stacked bar charts.

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Example Clustered Bar Chart
Figure 8.3. HIV prevalence rate among pregnant
15- to 19-year-olds at 4 clinic sites, City X,
Country Y, years 1 3
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Specific Rules Clustered Bar Charts

• Show no more than three sub-bars within a group
  of bars.
• Leave a space between adjacent groups of bars.
• Use different colours or patterns to show
  different sub-groups for the variables being
  shown.
• Include a legend that interprets the different
  colours and patterns.

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Histograms

• A representation of a frequency distribution by
  means of rectangles
• Width of bars represents class intervals and
  height represents corresponding frequency

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Example Histogram
Figure 8.4. Children living with HIV, District X,
2002
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Pie Charts

• A circular (360 degree) graphic representation
• Compares subclasses or categories to the whole
  class or category using differently coloured or
  patterned segments

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Example Pie Chart
Figure 8.5. Projected annual expenditure
requirements for HIV/AIDS care and support by
2005, by region
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Area Maps

• A graph used to plot variables by geographic
  locations

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Example Area Map
Figure 8.6. HIV Prevalence in Adults in Africa,
end 2003
Source UNAIDS, 2003
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Tables

• A rectangular arrangement of data in which the
  data are positioned in rows and columns.
• Each row and column should be labelled.
• Rows and columns with totals should be shown in
  the last row or in the right-hand column.

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Example Table
Table 8.1. Adults and children with HIV/AIDS by
region in Country Y, end year X
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In Summary

• Surveillance data can be analysed by person,
  place or time.
• Depending on your data, you can choose from a
  variety of chart and graph formats, including pie
  charts, histograms, tables, etc.
• Using several simpler graphics is more effective
  than attempting to combine all of the information
  into one figure.

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Warm Up Review

• Take a few minutes now to look back at your
  answers to the warm up questions at the beginning
  of the unit.
• Make any changes you want to.
• We will discuss the questions and answers in a
  few minutes.

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Answers to Warm Up Questions

• 1. List two demographic variables by which
  surveillance data can be analysed.

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Answers to Warm Up Questions, Cont.

• 1. List two demographic variables by which
  surveillance data can be analysed. Age, sex,
  marital status, etc.

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Answers to Warm Up Questions, Cont.

• 2. True or false? Compiling all the data into one
  comprehensive chart or graph is more effective
  than including many simpler diagrams.

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Answers to Warm Up Questions, Cont.

• 2. True or false? Compiling all the data into one
  comprehensive chart or graph is more effective
  than including many simpler diagrams. False

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Answers to Warm Up Questions, Cont.

• 3. Which of the following cannot be extracted
  from public health surveillance data
• a. changes over time
• b. changes by geographic distribution
• c. differences according to subjects sex
• d. none of the above

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Answers to Warm Up Questions, Cont.

• 3. Which of the following can not be extracted
  from public health surveillance data
• a. changes over time
• b. changes by geographic distribution
• c. differences according to subjects sex
• d. none of the above

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Answers to Warm Up Questions, Cont.

• Match the type of chart/graph with its example.

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Answers to Warm Up Questions, Cont.

• 4. Match the type of chart/graph with its
  example
• scale line graph d
• area map c
• pie chart a
• histogram b

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Small Group Discussion Instructions

• Get into small groups to discuss these questions.
  
• Choose a speaker for your group who will report
  back to the class.

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Small Group Reports

• Select one member from your group to present your
  answers.
• Discuss with the rest of the class.

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Case Study Instructions

• Try this case study individually.
• Well discuss the answers in class.

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Case Study Review

• Follow along as we go over the case study in
  class.
• Discuss your answers with the rest of the class.

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Questions, Process Check

• Do you have any questions on the information we
  just covered?
• Are you happy with how we worked on Unit 8?
• Do you want to try something different that will
  help the group?

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