Example of a boxplot for the variable Age
The box represents the interquartile range.
The line across the box indicates the median.
The "whiskers" are lines that extend from the box to the highest
and lowest values, excluding outliers.
The circles above our upper whisker represent the outliers.
The location of the box between the whiskers tells us how the
data are distributed. If the box is in the middle of the whiskers,
the data are probably more evenly distributed.
If the box is closer to the lower whisker, the data are probably
skewed towards the lower end of the scale. If the box is closer to
the upper whisker, the data are probably skewed towards the
higher end of the scale.
Example of a histogram
Example of a horizontal bar graph or bar chart
Using the correct scale in line graphs
When drawing a line, it is important that you use the correct scale.
Otherwise, the line's shape can give readers the wrong impression
about the data. Compare Figure 3 with Figure 4:
Figure 3. Number of guilty crime offenders, Grishamville
Figure 4. Number of guilty crime offenders, Grishamville
Using a scale of 350 to 430 (Figure 3) focuses on a small
range of values.
It does not accurately depict the trend in guilty crime
offenders between January and May since it exaggerates
that trend and does not relate it to the bigger picture.
However, choosing a scale of 0 to 450 (Figure 4) better
displays how small the decline in the number of guilty
crime offenders really was.
A multiple line graph can effectively compare similar items over the
same period of time (Figure 5).
Figure 5. Cell phone use in Anytowne, 1996 to 2002
Figure 5 is an example of a very good graph.
The message is clearly stated in the title, and each of the line
graphs is properly labelled.
It is easy to see from this graph that the total cell phone use has
been rising steadily since 1996, except for a two-year period (1999
and 2000) where the numbers drop slightly.
The pattern of use for women and men is similar.
In summary, line graphs
show specific values of data well
reveal trends and relationships between data
compare trends in different groups of a variable
Focus on Your Data!
Keep Graphics Clean and Simple
A lot Better!
Your job is to communicate clearly and directly with
your audience. Work to eliminate anything that
distracts from this.
Be sure you plot the relationship you want to show. If
you want to see the change in population through time,
the X-axis should be time and the Y-axis should be
population. Nothing else makes sense.
In the above example, only the two lines show your
data. The axes give the reader a sense of the range of
Presenting data...the good and the bad - an example of
a good and bad table.
binding Energy (eV) Intensity (Counts)
Table 3. XPS Intensities for Binding Energy of 275 - 276 eV.
How many problems can you find with this table ?
datapoint binding intensity
1 275.00002 4311
2 275.100030 4366.0000
3 275.20001 4380
4 275.30001 4436
5 275.40002 4578
6 275.50002 4673
7 275.60003 4684
8 275.70001 5191
9 275.80001 5371
10 275.90002 5453
Table III. Data points collected from the Shimadzu 270 (lab part 3B).
Example of a good and bad figure
How many problems can you find with the bottom
Figure 1. XPS data for CxPFOS
Chart A. The spectrum observed for group #6, sample
Some additional tips for preparing figures and tables:
All graph axes require labels that include
both the variable name and units.
Axes should use reasonable scales to clearly
show the data and have labeled tic marks.
The axis labels do not need to show the full
number of significant figures.
Table columns should specify the units
employed under each heading.
Use the results section to explain the purpose of
every figure, schemes, equation and table.
Published research results never include orphan
data, that is, information that is not explained or
put into context by the written text. This is also
a good rule to follow in lab reports.
When referring to a figure, table, or equation,
use its number in the text, for example:
A plateau was observed at reduced pressures
greater than 0.1, as indicated in Table 1.