First, to summarize using Wilkinson and Oliver's
point of view, JIT is characterized by high pervasiveness,
high immediacy, high internal substitutability and
low external substitutability; for JIT purchasing, only
external substitutability is considered, as internal
substitutability refers primarily to workers' polyvalence.
Qualifying JIT as highly pervasive is justified by
the fact that activities are so tightly linked together
that any disruption outside the core activities is likely
to affect these activities. JIT is also associated with
high immediacy because the reaction time is considerably
shorter than it is within a traditional production
and operation context. Buffer stocks are usually low,
suppliers are required to increase delivery frequencies
and decrease lot sizes, and within the production
process the lot sizes are also reduced and set-ups are
more frequent