| The LMVP data are typically graphed
in 3 different ways. The most common graph shows seasonal variations
(See 1 below). The parameter represented is named on the vertical
axis, which is usually on the left. These graphs will show all of
the data collected last year, with the date of collection shown
at the bottom of the graph.
Some data are shown as trend graphs. Depending upon the
amount of information we need to show we either use a stick plot
(2) or a box plot (3).
The stick plot features a “stick” that reaches from
the high value to the low value and a dot that shows the geometric
mean for that year. Box plots convey a bit more information than
stick plots. The “caps” at the top and bottom show
the maximum and minimum values for the year. The “box”
surrounds the middle half of the data. Finally, the line within
the box shows the median, or middle, value.
For more information on box plots, visit:
http://www.lmvp.org/boxplots.htm.
Each stick or box plot represents data from a single season.
These plots will always be shown with other stick or box plots
for comparison among years. When stick plots or box plots are
shown, only the “summer” data are used. For our purposes,
we define summer as the period between May 15 and September 15.
This period is shown in section 1 of the figure below with the
dotted lines, so in this case the samples from early May and early
October would not be used. Trimming the data like this lets us
compare data from different years, regardless of whether the volunteer
began (or finished) sampling early (or late).
In the stick and box plots below, the take home point is that
the data range from a low of 13 to a high of 32 ug/L, but most
of the values are at the lower end of that range. You can tell
this because the dot (in the case of the stick plot) and the median
line (for box plots) are closer to the bottom than the top. |
