Control Treatments


 Specific treatments to include in a set of trials
will depend upon the factors being studied and the
combinations of levels needed. Whenever possible,
regional trials should include the following treatments as
controls:
 1) At each site the individual farmer's own
 technology for the crop;
 2) Technology representative or typical for the
 crop in the recommendation domain; and
 3) The currently recommended technology for the
 recommendation domain.

 The first control is to give each farmer a basis for
comparison and to provide researchers an estimate of
experimental bias. (Is yield within the experimental area
at each site greater or less than the farmer's yield?)
The second control compares the typical practice in the
region with the other treatments. This second control,
when used unchanged year afer year, serves also as a
benchmark to evaluate the year effect for trials conducted
dver time. A third control, representing the current
recommendation, is included to see how the new technology
being studied compares. The second and third controls
provide control conditions for all remaining treatments.
If the treatments are considered additive to present
practices, the second control provides these conditions.
If the treatments are considered as additive to
recommended practices, the third control provides these
conditions.

Kinds of Treatments

 Analysis of the data should be anticipated when
choosing treatments. Care should be taken to assure that
necessary comparisons can be made readily and that
differences may be found if indeed they exist. For
quantitative variables, the total range and the spacing
between levels should be carefully chosen to assure that
the treatment range will provide the response desired and
that regression may be estimated with adequate precision.
Equal spacing of the levels, although recommended and
convenient from a statistical point of view, is not always