Select the best answer
Corn variety 1 yielded 140 bushels per acre last year at a research farm. This year, corn variety 2, planted in the same location, yielded only 110 bushels per acre. Unfortunately, we don’t know whether the difference is due to the superiority of variety 1 or to the effect of this year’s drought. This is an example of
(a) bias.
(b) matched pairs design.
(c) confounding.
(d) the placebo effect.
(e) replication.