What is the best way to illustrate variability?
If you measure all of the trees in a population, say at the BFEC, the mean you calculate is the "true"
mean of that population, and the variability represents biological differences in the trees. Now, if you wanted
to extrapolate to all one-year old Pinus strobus in the world, the calculated mean is unlikely to be the
"true" mean. For this reason, when means are presented, they are generally presented +/- some measure
of variability along with the sample.
- Standard Deviation -
is a measure of the amount of variability present in a sample. Click
to see a graphic representation of standard deviation. Two samples can have the same mean, but can differ
in the amount of variability they represent.
- Standard Error -
represents the variability in a sample scaled to the sample size.
- 95% Confidence Interval -
is the range over which you would expect the mean to lie 95% of the time upon repeated sampling of the same population.
How do the above measures of variability compare?