We now describe how this additional structure is captured in a single ranked set
sample of k measured observations. First, an initial simple random sample of k units
from the population is selected and subjected to ordering on the attribute of interest via
some ranking process. This judgement ranking can result from a variety of
mechanisms, including expert opinion, visual comparisons, or the use of easy-to-obtain
auxiliary variables, but it cannot involve actual measurements of the attribute of interest
on the sample units. Once this judgement ranking of the k units in our initial random
sample has been accomplished, the item judged to be the smallest is included as the first
item in our ranked set sample and the attribute of interest will be formally measured on
this unit. The remaining k-1 unmeasured units in the first random sample are not
considered further. We denote this measurement by X[1], where a square bracket [1] is
used instead of the usual round bracket (1) for the smallest order statistic because X[1] is
only the smallest judgment ordered item. It may or may not actually have the smallest
attribute measurement among our k sampled units. Note that the remaining (other
than X[1]) units in our first random sample are not considered further in the selection of
our ranked set sample or eventual inference about the population. The sole purpose of
these other k-1 units is to help select an item for measurement that represents the
smaller attribute values in the population.