Using a statistical perspective, we often find it useful to regard all these
influences together (along with many others that we may be unaware of) as a global
process that turns out readers of different capabilities. In the sense that we cannot
know how these various factors work together in practice to produce results, the
global process is a probabilistic one, unpredictable at the micro level. However,
even though readers produced by this process vary unpredictably in their
performance, we can regard the entire process at any given time as having a certain
stable capability to produce competent readers. The average performance of a large
sample of readers produced by this process is one way to gauge the power of that
process (or its propensity) to produce a literate citizenry.