One-at-a-Time Plans

One-at-a-time experiments are always done when the experimental system is set up to produce single results or pairs of results. When random error is small compared to main effects expected, such experiments are economical, but may give biased estimates. These biases can usually be described by two-factor interactions (2fi). Minimal augmentations of standard one-at-a-time sequences are given, first to separate main effects from 2fi, then to estimate each 2fi separately. Each new datum produces one or more new estimates.