Missing plots. Frequently in on-farm research,
animal intervention or other unusual occurrences can ruin
one or more plots in a trial. A decision must be made by
the researcher on how to adjust the trial to account for
these missing data. There are several ways to do this:
generate a value for the affected plot, drop the block or
replication from the analysis, or analyze all remaining
plots as if they were a fully randomized design with
unequal numbers of replications. Still another
alternative, if the plot is not completely destroyed, is
to harvest the parts of the plot that are undamaged and
proceed as for missing plants (see next section).
 If fewer than four replications were used in the
original design, dropping an entire replication is a
fairly drastic measure, and other alternatives should be
considered. If only one or two plots were affected and
there were several treatments in the trial, then
generation of estimated values would be the best
alternative. If regression rather than analysis of
variance is to be used to analyze the data, then a missing
plot is less of a problem and may be omitted without
significantly affecting the analysis.
 Standard statistical texts recommend a procedure not
too complicated for field use, if only one, or at most
two, plots are missing. For a randomized complete block
design a single missing plot value can be estimated by the
following equation:

 Y = (bB + tT G) / (b 1)(t 1)

where b and t are the numbers of blocks and treatments,
respectively, B and T are totals of observed plot values
in the blocks) and treatments) containing the missing
information, and G is the grand total of all observed plot
values. The calculated or estimated value Y is entered
into the data where the plot was missing. Analysis of
variance is performed as usual, except that one degree of
freedom is subtracted from total degrees of freedom (and
therefore error degrees of freedom will also have one less
than if the plot value had not been missing). Treatment
sum of squares will have to be reduced by an amount equal
to:

 [B Y(t 1)]2 / t(t 1)