Statistical calculations: Measures of central tendency and
variability  Measures of central tendency  In the example of
measuring the length of a frond (leaf) in a bracken fern
population, measurements were made of the length of 100 bracken
fronds. Ideally the 100 fronds represent a random sample of the
bracken population. The data are presented as the frequency of
measurements in a series of 10 cm size classes so that
measurements are to the nearest 0.1 metre.  Size class (m)  No.
of fronds in size class  Cumulative frequency
There is considerable natural variability in the length of
bracken fronds. There are three different measures of central
tendency we could report for this data:  The mode: the size
class that had the highest frequency (the most popular size) =
1.3m  The median: the middle value (half the measurements are
above it and half below) = 1.2m  The mean: the sum of all the
readings divided by the number of readings = 1.1m  Another
method that is used in conjunctio