bar graph histogram line graph pie chart
Data presentation is an important communication tool. Graphic and tabular representations of your results can enhance your arguments about your hypothesis or it can totally confuse them. Graphing is the process of making a figure. Figures and tables are used throughout the scientific literature to convey information about data obtained during an experiment.
bar graph
histogram
line graph
pie chart
Bar Graph is useful to compare discrete variables, such as differences in sex.
Histograms are useful for comparing categorical data, such as age groups.
Line graphs are useful for all types of continuous variables, such as growth.
Pie graphs are useful for percentage data, such as distributions within a population.
Key Points about Graphing
1. Keep it as simple as possible, while still conveying your idea.
2. Don’t try and crowd too much on to a graph.
3. Label all axes including units of measure and avoid abbreviation.
4. Make scales of measurement easy to read; don’t crowd numbers. Use multiples, e.g. 2, 5, 10, 20, 25, 50, 100s as appropriate for the data.
5. Be sure that the increments are placed proportionally. The distance between 0.5 and 1 should NOT be the same as between 5 and 10.
6. If possible label lines directly, if not, use a legend. This goes along with 2 above.
7. Avoid using colors, black and white offers good contrast. Colors are fine for lectures and seminars, but for most publications (it’s expensive.)
Where to place information
1. Independent variables, especially time, should be on the horizontal or X axis. Dependent variables should be placed on the vertical or Y axis.
2. Label the variables and list the units of measure, e.g. mL, g, mm, etc.
3. Use tic marks between numerical intervals to reduce crowding.
4. Use shading or patterns instead of colors.
5. Label lines directly when there is room, if not use a legend.
6. Use different line types or point shapes, instead of color.
7. Standard technical writing style places the caption for Figures below the data, and the caption for Tables above the data.
Captions should briefly describe the data presented in a figure in 3-5 sentences
1. Figure captions begin with "Figure" followed by a number. Thus, the first figure in a report should be, Figure 1.
2. The first sentence should state the relationship between the independent and dependent variables.
3. The next sentence or two (no more) should be important results that you want the reader to focus on. This sentence should be written quantitatively. You will expand on these sentences in the Results and Conclusion sections in your lab report.
4. The last sentence should inform the reader on what the data represent statistically, such as averages based on three replications.
Avoid: Germination in light vs dark. Captions for figures should NOT be written as if you were advertising a billboard for a title weight fight or world wrestling match!
Vague: Figure 1. The effect of light and dark on seed germination.
Informative: Figure 1. Percent germination in the radish variety cherry belle germinated with and without sunlight. Without sunlight, 85% of the radish seedlings germinated compared to only 47% germination in sunlight. Data are averages from three replications.
Figures, like tables, should be consecutively numbered and referenced in the results narrative at the end of a sentence in ( ) before the period, or directly referred to in the text.
Refering to a figure within the text of a report
Preferred: Germination of seeds in the light was reduced 60% compared to seeds germinated in the dark (Figure 1).
Suitable: In Figure 1, germination of seeds in the light was reduced 60% compared to seeds germinated in the dark.
A completed figure should resemble one similar to this one.
Figure 1. Radicle growth of Alaska and Little Marvel peas over two weeks. Radicles of Alaska peas grew 40% more than the Little Marvel peas after two weeks. Radicles of Alaska pea reached an average length of 50mm compared to 30mm for Little Marvel. Data are the average length of radicles from five replications.