facilitates the use of more locations.
 If a sufficient number of locations have been used
for site-specific trials, and if they have designs and
treatments in common, they can be analyzed as regional
trials -- a cost-effective utilization of information.
Usually though, a trial will be designed especially for
regional analysis with fewer treatments than typical
site-specific trials but with a design common for all
sites. Variables included in regional trials, then, can
be the same as those that were included in site-specific
trials, a subset of them, or others based upon different
criteria.
 The methodology of combining an analysis of variance
of data from all locations permits a measurement of the
interaction of technology with environment. It also
allows for a statistical interpretation of the relative
stability of each technology by a partitioning of the
total degrees of freedom due to treatments, and for
utilizing regression techniques involving environmental
indexes (see Chapter VII for a description of modified
stability analysis).
 Farmers' participation in these trials contributes to
the researchers' focus on the farmers' reality, allowing
adjustments in experimental design and generating
conclusions that would not be possible from a strict
numerical interpretation of resulting trial data. For
example, farmers could readily reject the color or shape
of an experimental bean cultivar in a variety trial, or,
in the case of maize, point out the inadequacy of husk
coverage, or the impossibility of a suggested thinning
practice because of local religious beliefs.

DESIGN AND METHODOLOGY

 Technologies to be evaluated in regional trials
usually are selected on the basis of results from
exploratory and site-specific trials conducted during the
previous year or years. Perhaps such trials were
concerned with individual components, such as variety,
fertilizer, or insecticide. In regional trials these may
be combined into a more comprehensive system. From all
previous trials in a region, a consensus is formed by a
multidisciplinary team as to what factors need to be
researched on a broader basis.