Tables, graphs, and diagrams

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Tables, graphs, and diagrams

• Preben Aavitsland
• Vladimír Príkazský
• Viviane Bremer

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Tables, graphs and diagrams.

• organise
• summarise
• display
• ...data from outbreaks, surveillance and studies

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Uses of tables, graphs and diagrams

• Effective presentation
• to the professionals
• to the public
• Easy interpretation
• Visual examination
• Analysis

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Paper vs. screen

• Paper
• Time unlimited
• Repetition
• Details
• White, grey and black

• Screen
• Time lt 1 min
• No repetition
• Less details
• Colours possible

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Tables, graphs, and diagrams

• Self-explanatory
• Simple!
• Title
• what, who, where, when
• Define abbreviations and symbols
• Note data exclusions
• Reference the source

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Type of variables

• Quantitative
• Discrete
• counts, dates, cases,...
• Continous
• height, Hb, .

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Type of variables

• Qualitative
• Dichotomous
• sex, ill/not ill, .
• Nominal
• religion, nationality, eye colour,...
• Ordinal
• social class, cancer stage, .

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Tables
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Types of commonly used tables

• One-variable tables
• Frequency distribution
• Multivariable tables
• Contingency tables
• 2x2 tables

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Tab 6. Distribution of cases of salmonellosis
(n65) by age group. Hospital A, Dublin, August
2006
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Table 9. Gonorrhoea by age-group and sex, Norway,
2005
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Tab. IV Fish consumption and gastro-intestinal
illness among customers at Uncle Mikes Fish
Chips, Berlin, 2005
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Tab. IV Gastrointestinal illness and fish
consumption among customers at Uncle Mikes Fish
Chips, Berlin, 2005
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Table from a case control study (paper) Tab. IV
Gastrointestinal illness and fish consumption
among customers at Uncle Mikes Fish Chips,
Berlin, 2005, n124 (2 cases were excluded)
explanation of symbols - we measured, no
case in this category, we cant say that it is
0 . we measured, but we cant calculate the
average of 1 case
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In tables...

• Labels for rows and columns
• Totals for rows and columns, usually
• Units of measurements
• Max five variables
• Horizontal lines OK, vertical not

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Graphs Diagrams
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Types of commonly used graphs

• Line graph
• Arithmetic scale line graph
• Semi-logarithmic scale line graph
• Histogram
• Epidemic curve

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The arithmetic-scale line graph 1
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The arithmetic-scale line graph 2

• For time series
• Show actual changes in magnitude
• X-axis time
• Y-axis incidence (or number) of cases
• Start at 0
• Breaks possible, clearly marked

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The semilogarithmic-scale line graph 1
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The semilogaritmic-scale line graph 2

• For time series when
• interested in rate of change
• X-axis time arithmetic
• Y-axis rate (or number) of cases, logarithmic
• Straight slope constant rate of change
• Steep slope constant rapid change
• Parallell lines same rate of change
• Change in slope acceleration ? deceleration of
  rate
• Start at lowest cycle, e.g. 0.1-1 or 1-10
• No breaks

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The epidemic curve 1 Cases of salmonellosis
(n65) by date and time of onset of illness.
Hospital A, Dublin, August 2006
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The epidemic curve 2

• Histogram
• Area proportional to number
• No space between columns
• One population
• X-axis time
• Start before epidemic, continue after
• Interval 1/4 of incubation period
• Y-axis number of cases
• Usually one square one case Easy to make
  in Excel

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In graphs...

• Labels for axes, scales and legends
• Legends or keys if gt1 variable
• Scale divison, appropriate scale
• Units of measurements in title
• No grid, no numbers
• No 3D

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Types of commonly used charts

• Charts based on length
• Bar charts(horizontal, vertical, grouped,
  stacked)
• Charts based on proportion
• Component bar chart
• Pie chart

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Grouped bar chart
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Stacked bar chart
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Component bar chart
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Bar charts

• Order
• Natural
• Decreasing or increasing
• Vertical or horizontal
• Same width of bars
• Length frequency
• Space between bars and groups, but not within
  groups
• Tables are often better

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Pie chart
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The area dot (or dot density) map
Figure 2. Cases of meningococcal disease in
Dublin 2006 by area of residence. 1 dot 1 case
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The spot map
Figure 1. Cases of meningococcal disease in
Dublin 2006 by place of residence. 1 dot 1 case
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The area map
Figure 3. Incidence per 100,000 of meningococcal
disease in Dublin 2006 by area of residence.
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Think data-ink

• Every bit of ink should have a reason

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Designing graphics

• Show the data
• Use ink for the data
• Remove unnecessary ink
• Remove gimmicks
• No 3D
• Careful with colours

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Summary

• Use graphics to explore and present data
• Think of difference between paper and screen
• Think of your message and choose the graph type
  accordingly
• Save your ink!