Appendix A: Graphing


 

For graphic presentation of results, the following rules should be observed:

 

  1. Use graph paper to plot the values accurately.
  2. Plot the independent variables on the X-axis and the dependant variable on the Y-axis.
  3. Each axis must be LABELLED, the units indicated and the axes lines drawn.
  4. The intervals on each axis should be EVENLY SPACED and APPROPRIATE for the range of data so most of the area of the graph can be used. For example, if the highest data point is 147, the highest value labelled on the axis might be 150. If you labelled intervals up to 200, there would be a large unused area on the graph. When drawing bar graphs, each bar should be of the same interval and width.
  5. Generally, begin both axes of the graph at zero in the bottom left corner. The zeros should always be labelled.[1]
  6. Always use a RULER and a PENCIL when drawing graphs. It is important to be as neat as possible. DO NOT USE COLOUR.
  7. Always include an N-value with your graph e.g. N = sample size. This is typically included in the legend or caption.
  8. Choose the type of graph that best presents your data. Line graphs and bar graphs are most frequently used.

 

Line graphs show changes in quantity of the dependant variable and emphasize the rise and fall of the values over their range. Use a line graph to present continuous data. When drawing best-fit lines, you do not have to go through any of the points.

 

If you are plotting more than one curve, the data point from each curve should be plotted with different symbols.

 

 

BAR GRAPHS are constructed like line graphs except that a series of vertical bars are drawn from the datum to the x-axis. Bar graphs are often used for data that represent separate or discrete groups. For example, the graph to the right illustrates the differences in height of males and females in Biology 111.

 

Note that categories on the x-axis (bins) are separated by some space, i.e. there are eight bars on this graph, though they are presented in four groups of two.

 

 

 

 

 

 

 

 



Appendix B: Captions


 

The amount of information in a caption is context sensitive, but is usually more than most students think. The caption for a graph will have different information than that for a map; however, the caption’s job is to explain to the reader what is illustrated; we do not use the word “title” synonymously with “caption”.

 

  1. Placement
    1. Tables: The caption goes above the table.
    2. Figures: The caption goes below the figure. “Figures” include photos, drawings, graphs, maps…essentially, anything but a table.
    3. In all cases, justify your caption to the left.

 

  1. Content
    1. Always start with “Figure 1” or “Table 7”, as appropriate.
    2. In general, the caption should describe to the reader what the author wants the reader to see from the figure or table, without going into the detail which is reserved for the body of a report.

·     A key to symbols is sometimes in the caption (if not, there would be a legend with the same information)

    1. Avoid starting out captions with the following phrases:

A map of…                               A table of…

A diagram of…                         A graph of…

If it isn’t obvious to the reader that you’re illustrating a map (for example), without being told that this is “A map of…”, then the reader is not qualified to read this material.

    1. Some things to include under specific cases:

                                                              i.      microscope images or drawings

·        type of preparation

·   e.g. whole mount, wet mount, section [which plane], smear

·        key to symbols (if necessary)

·        species


                                                            ii.      graphs

·        error bar interpretation (e.g. standard deviation, 95% Confidence Limit…), if necessary

·        sample size (this is sometimes placed elsewhere on the graph)

                                                          iii.      tables

·        sample size

·        the column heading of tables usually allow for easy interpretation, so little more than a standard description is needed

  1. Other stuff

If there are two graphs or pictures which are closely related, they should appear within one figure, with the two being labelled (a) and (b); one caption is used to refer to both.

 

For example, students were asked to measure the length of two axes on scallops. This was done to determine if the height and length of the shell grow uniformly relative to one another. The data are shown below, with a single, suitable caption covering both graphs.

 

 



[1]    To avoid generating graphs with wasted space, you may signify unused graph space by two vertical tic marks between zero and the lowest number on one or both axes, or simply start the labelling of each axis at a higher number.