An experiment with insecticides
Scientists investigating chemical control of brown plant hoppers and stem borers in rice, conduct an experiment to compare the effectiveness of six different foliar and granular insecticides (Source: Gomez & Gomez (1984) Statistical Procedures for Agricultural Research.).
The following experiment was designed:
Treatments: 6 different insecticides plus a control treatment (different numbers/colours in the figure).
Experimental units: 28 field plots.
Replications: each treatment (including the control) was randomly allocated to 4 out of 28 plots.
Response variable: rice yield (kg/ha).
No restrictions were imposed on the randomization, each plot had the same probability of receiving a particular treatment.