EASA-450 Scientific Communications, Spring 2004

Martha Davis - Chapter 11, Presenting Data

Tables, Graphs, Charts

1. Considerations

As usual, the needs of the audience will dictate the style of the presentation. Let’s assume you have obtained some data from an experiment, and you wish to include it in a table. You have 4 basic choices:

•  Insert it in the text as you write. This is good for small amounts of data only, e.g. up to about 3 values. Example: “For temperatures of 250 and 300ºC we recovered 60 and 80% of the ⁴⁰K  respectively.”  
  

•  Make a table. This is required if you want to record the exact measurements as part of the scientific record, particularly if differences between your own work and that of other authors needs to be compared numerically.
  

• Make a graph (i.e. a figure). This is appropriate if you want the reader to quickly grasp the main points of the data (trends, variability) and the exact values are not critical to understanding. Figures (graphs or charts) are the most efficient way to display data in a semi-quantitative way.  
  

•  Make a table in an Appendix. This is useful if you need to record specific values, but to do so in the body of the text would be too much of a distraction. Frequently this is required in theses, where there is sometimes a large amount of data.

To decide which format to chose, Ask yourself the purpose of each table or figure:

•  which layout gives readers the quickest, most intuitive feel for the information?

• are there any restrictions on using tables and figures (cost, space)?

• is the document to be used later as a reference?

• is the graphical information to be used quantitatively or qualitatively?

2. General Guidelines

• tables and figures should be placed in the text just after their first reference

• all elements of the table or figure should be legible

• does the information need to be included as part of the text, or is it supplementary?

 3. Types of Information

• dependent – information that is part of the text and depends on it for explanation

• independent – a table or figure that has a caption that makes it self-sufficient

 Generally if the element is supposed to be an informative summary of information, it should be included along with the text (on the same or following page). If the information is more of a detailed record, it should go in an Appendix. Make sure that if you include a figure or table that its contents are thoroughly discussed – do not simply say ‘The results are shown in Figure 5.’ and then go on with another topic!

4. Elements 

Tables and figures have a number of elements that can be manipulated:

• numbers – mostly in tables, figure axes

•  words – appear everywhere

•  lines -  especially rules in tables

•  shapes -  e.g. symbols for figures

•  spaces – can help in alignment

•  captions – for both tables and figures

5. Tables 

• dependent tables do not need a caption, they act just like a small formatting change from regular text. In-line tables are usually small.

•  independent tables can be open – i.e. not ruled at all, semi-closed – ruled partially, or closed – ruled along all aligned elements.

• when choosing between horizontal or vertical ruling (lines), note that the eye needs more help with the horizontal direction than with the vertical

• leaving spaces (‘blocking’) can be as effective as horizontal or vertical lines

• spaces can help with the headings but not generally within the body of the table

• missing values – do not leave a ‘-‘, it is ambiguous and meaningless. Use instead a 0 – if you mean zero, or if there is no value assigned to that cell put in a symbol (e.g. ‘*’) and explain the symbol in a caption.

• captions normally come at the top of the table, underneath the title.

6. Charts

A chart is a term used widely in the corporate world to signify graphical information. It is usually some type of bar chart, in which the length of graphical symbols denote values. As you can see when using a spreadsheet program such as Excel, there are many different types available:

• column, line, bar, pie, scatter, area, radar, doughnut, surface, bubble, stock, cylinder, cone, pyramid,

• each type can come in various flavors, some of these are:

  clustered, stacked, horizontal, vertical, left, right, 2-D, 3-D

 Your choice should be based on need and intuition. It is usual when designing the layout to have time and distance variable from left --> right, and to have positive variables plotted above the horizontal axis.

 Histograms are special charts where the frequency of occurrences is plotted as the ordinate and the abscissa are the events themselves.

7. Graphs / Figures / Plots

These terms are used somewhat interchangeably.

• graph (graphical, to graph) is a display object for data, either numerical or other

• figure (only used as a noun) is similarly to a graph, but is used more generally to refer to any kind of visual display. In science we use exclusively the term ‘figure’ to refer to displays, as in ‘Figure 3 shows the results .’. Whether ‘Figure’ gets shortened to ‘Fig.’ often depends on the Journal.

• plot (to plot) should be used as a verb to indicate act of displaying data, e.g. ‘we plot the ages against Th concentration in Figure 4’. Do not say ‘ as can be seen in the next plot’.

The essentials of any figure are:

•  labeled axes  

• legible elements (numbers, values, legends)

•  an informative caption (assuming an independent figure)

Graphs are almost always independent. They have the following elements:

• Axes – choose the appropriate scale, labeling, limits, units (remember that the unit is singular)

• Do not include more decimals or significant figures except in unusual cases. Tick marks should be rounded to the nearest whole unit.

• Elements – lines, curves, symbols, error bars; be careful when using different type of lines (dashed, dotted, dash-dot) because they do not always reproduce well.

• Caption – should allow the figure to be self-evident to the reader. It may not be possible to include all the details required to understand the figure, so a reference should be made to the text.

• Tips – Put essential information where it is clear, on the graph itself if possible. Reduce the need to cross-reference symbols and text with the caption (except when unavoidable).

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