Is a frequently used variant of simple random sampling. When performing systematic sampling, every element from the list is selected from a randomly selected starting point. For example, if we have a listed population of 6000 members and wish to draw a sample of 2000, we would select every 30th (6000 divided by 200) person from the list. In practice, we would randomly select a number between 1 and 30 to act as our starting point.  

The organisms or species that fills a systematic category. The Linnaean taxonomic units are species, genera, families, orders, classes and phyla.

A measure of how far a set of numbers is spread out around their mean. It corresponds to the sums of squares of the deviations of the observations to the mean, divided by the number of observations minus 1.

A web-based, simulated environment where users interact via motionable avatars; ie. graphical images that represent people.