GROUPING FARMS INTO
 RECOMMENDATION DOMAINS

 Introduction

In the previous exercises, we have been looking at all the farms as a
single group. Any recommendations made from these analyses would
presumable apply to all the farms in the sample and all other similar
farms. However, it is evident from the data in Exercise FAI that the
farms (or at least the fields) where the trials were conducted are
quite different. The environments in the fields from farms 1, 5 and
8, for example, are obviously poorer for producing maize than are the
environments in the fields from farms 3, 4 and 7. Unfortunately, as
mentioned in the introduction to these exercises, no information is
available on the characteristics of the environments at these
locations. We do not know if the lower yields are associated with
less rainfall, poorer fertility, late planting, less effective
weeding, or what. But we do know that for some reason there are
distinct environmental differences in the fields and on the farms
where these trials were planted. Even though these differences are
real, and form the real world of the farmers, they are the reasons
that many researchers complain about doing research on farms.

Without minimizing the importance of characterizing each environment
where on-farm trials are conducted, there is a convenient means
available to quantify the evident environmental differences. This is
to convert the overall farm (field) average (over all treatments) into
an index that reflects quality of the environment in each field and
differentiates it from the environments in other fields. Thus for
example, for farm (field) 1, the average yield is 2710 kg ha'1. This
converts into an index (without units) of 2710. The index for farm
(field) 2 is 4140. It is quite obvious that environment 2,
representing farm or field 2, with an index of 4140 is a better
environment for producing maize than environment 1 with an index of
2710. Even though some statistical purists feel the use of this index
in regression is marred, it has been in use for over 50 years and has
been invaluable in the absence of any other available method.

We will use the term El for this "environmental index." In the first
exercise that follows, El will be used in conjunction with the
production function. In later exercises, it will be used as an
important component in Modified Stability Analysis.