TABLES AND GRAPHS
Tables and graphs are the most common visual aids. Used extensively in all types of technical.writing, they are easily constructed from many available software programs. This section explains how to construct them and when to use them.
The information in tables and graphs is either an independent or a dependent variable. An independent variable is the group you are discovering information about. The dependent variable is the category you use to find out about the independent variable. The dependent variable changes when the independent variable changes. In a table: of weather conditions, the independent variable is the months. The dependent variables are average temperature, average precipitation, and whatever else you might wish to compare. The following sections tell you where to place these variables in tables and graphs.
Tables present information – usually numbers, but sometimes word sin columns and rows. A table shows classifications and relationships of numerical or verbal data. Here are some general principles for presenting tables.
- In general, use tables with more professional, expert audiences. Remember that tables are harder for less knowledgeable readers to understand.
- Refer to the table in the text.
- Point out the essential relationships you want readers to understand. Use a table when you must present all the numerical data to expert audiences so that they see the context of the relationships you point out.
- Use ab able to compare many numbers or features (and eliminate the need for lengthy prose explanations).
- Pu t the items you want to compare (the independent variables) down the left side of the table in the stub column. Put the categories of comparison (the dependent variables) across the top in the column headings. Remember, columns are easier to compare than rows.
- Use plenty of white space between columns and above and below the table.
- Give each table a number and a clear, concise title.
The following table shows the elements and organization of a table.
Production Rates and Labor Costs
Note: Labor contract will expire Jan. 1.
‘Rounded to the nearest cent.
“Based on 1 man working at S7.DO/hour.
‘Based on 1 man working at 58.3D/hour.
dl Cycle = 20 seconds for cutting + 90 seconds iot assembly
= 110 seconds.
<Based on 1 eight-hour shift.
SOllrce:.Production Department figures for first quarter.
Guidelines for Constructing Tables
The following detailed guidelines explain how to present material in a table. The guidelines progress through a table from top to bottom. Table 1 above illustrates all of these guidelines.
- Number tables consecutively throughout a report with Arabic numerals in the order of their appearance Put the number and title above the table. Us}: the “double number” method (for example, 2.3) only in long reports that contain chapters.
- Use the table title to identify the main point of the table. Do not place punctuation after the title.
- In general, use three horizontal rules and no vertical rules. If the report is more informal, use fewer or no rules.
- Name the independent variable in the heading of the left-hand column. Name the dependent variables (the categories you are comparing) in
the column heads.
- Use a spanner head to name the column headings below it. Spanners reduce repetition in column heads.
- Use a heading to identify the contents of the horizontal row of data to the right.
Cite the source of the data – unless it is obviously data collected for the paper. Either say “Source: Production Department figures for first quarter” or, if the table has been printed elsewhere, give a citation. Place explanatory comments below the bottom rule. Use the word Note followed by the comment. Use specific notes to clarify portions of a table. Indicate them by raised lower-case letters within the table and at the beginning of each note.
A graph can present in simplified form the same statistical data as a table. Many software programs allow you to enter data as a table and then convert it into many different kinds of graphs. Bar graphs, pie charts, and line graphs present information more dramatically than tables, though often not as specifically. Since graphs are more dramatic but less precise, you should determine whether a table or a graph is more appropriate for your readers’ needs.
Guidelines for Selecting a Graph
If you decide to present your information graphically, you must determine whether a bar, pie, or line graph is best.
- Use a line graph to depict trends or relationships. In a trend, the same data change over time. The population figures for one city at different points in time is an example of a trend. A relationship shows the interaction of two variables, for example, percentage of pollutant to size of latter.
- Use a be graph to compare discrete items. For example, the population of three-different cities at one point-in time can be shown using a bar graph.
- Use a pie chart to represent discrete values as parts of a whole. If you
want to compare profits to total income, use a pie chart.
- Research shows that bar graphs are the easiest for less knowledgeable readers to grasp.
Guidelines for Presenting Graphs
The following guidelines explain how to present the title and number of graphs clearly.
- Refer to all graphs as figure s, and number them sequentially through out the report, using Arabic numbers
- Place the word Figure (or its common abbreviation Fig.) and the number
at the left-hand margin.
- Treat the word figure consistently. Either use all capital letters or capitalize just the first letter (Figure). Place a period after the number, if the title follows on the same line. If you place the title underneath the number, do not use a period.
- Place the title after the number or below it. Both methods are used. Do not underline the title; do not use a period after it; use initial capitals only, followed by lower-case letters.
- In informal reports, writers place the title either below (as in this book) or above the figure, whichever is dearer in the page makeup. (Many software programs automatically place the titles above the figure.) .
- If needed, start a second line directly under the first letter of the title. Indicate the source of the data by placing the word Source under the figure, followed by the citation.
- Refer to the graph in the text. Point out the relationship you want readers to understand.
A bar graph uses rectangles to indicate the relative size of several variables. Bar graphs contrast variables or show magnitude effectively. (See Figure 7.1.) A bar graph compares the items by means of the height or length of the appropriate .bars. Bar graphs can be either horizontal or vertical, depending on whether the bars go up the page or across it.
TONS OF AIR FREIGHT
(thousands of tons)
SOlaCt’: 1986 Program Strategies. Reprinted by permission of the City of Dayton, Ohio.
Vertical bar graphs (frequently called column graphs) are better for showing discrete values over time, such as profits at certain intervals. Either typecan be used in most other instances. The following guidelines explain how to construct bar graphs more . effectively: These guidelines are for vertical bar graphs. Rearrange items accordingly for horizontal bar graphs.
- Place the names of the items you are comparing – the independent variable – under the bars (for a vertical bar graph).
- Place the units of comparison – the dependent variables (usually numbers) – at the left.
- Make the spaces between the bars one-half the width of the bars. (Many computer programs do not follow this guideline.) Use a legend – a small sample of the markings and brief phrase to explain the meanings of the bars’ markings.
Notice how the bars in Figure 7.2 are subdivided to show an additional comparison of percentages. Figure 7.3 shows a multiple bar simple where
CONVENTION CENTER BUILDING REVENUES
These figures include building rental fees only.
Concession fees are not included.
Divided Bar Graph
Source: 1986 Program Strategies. Reprinted by permission of th c City of Dayton, Ohio.
EMPLOYMENT BY SECTOR
Figures are adjusted to reflect changes in the Metropolitan Area.
Multiple Bar Graph
Source: 1986 Program Strategies. Reprinted by permission of the City of Dayton, Ohio. more than one bar is used to compare quantities; this device is useful when the comparison must extend over several years. Notice the legends in Figures
7.2 and 7.3.
A line graph shows the relationship of two variables by a line connecting points inside an x (horizontal) and a y (vertical) axis. These graphs usually show trends over time, such as profits or losses from year to year. The line connects the points, and its ups and downs illustrate the changes’- often dramatically. Choose a line graph if you want to emphasize continuity; choose a bar graph if you want to emphasize the relative size of each item. shows the public’s perception of park safety over a series of years. The ratings of increases and decreases in park safety are ·easy to grasp. Notice that percentages appear at each year to indicate precise numbers. The following few general guidelines show how to make line graphs more effective . Name the independent variable – the one that changes automatically such as years – on the horizontal axis.
Source: 1986 Program Strategies. Reprinted by permission of the City of Dayton,
(for major Ohio metropolitan areas)
Multiple Line Graph
Source: 1986 Program Strategies. Reprinted by permission of the City of Dayton,
- Name the dependent variable – the one that changes because the independent variable changes, like profits – on the vertical axis. If m ore than one line appears in the graph, use a legend to explain each.
- Don’t use too many lines. If you use several lines, make them ‘visually distinct (for example, use a dotted line and a continuous line.
In Figure 7.5, a multiple line graph, several lines compare the same information (unemployment rates in several cities) over the same time period. A legend explains what each line stands for.
A pie chart uses segments of a circle to indicate each segment’s percentage of a total. (See Figure 7.6.) The whole circle represents
HOUSING AND ZONING CASES
TOTAL CASE LOAD