// instruments · n of one
n of one
A single-case experiment on one routine. One change, one daily measure, a baseline, a fixed run, a reversal rule, a success line — all written before the change starts. Fill the fields, print the card, record by hand. The print is the save; nothing is stored, nothing is sent.
// the change — one sentence, one variable
// the measure — chosen before starting
// recorded when — same time every day
// start date — day 1 of baseline
// baseline days
// run days
enter a start date — the change-start and decide-by dates are computed from it
// the reversal rule — decided now, applied later
// the success line — what result keeps the change
// n of one · protocol — written before starting
the change, in one sentence
// recording grid — one number a day · b = baseline, d = run
one variable · measure and reversal rule fixed before day 1 · single-case design (Barlow & Hersen, 1984; Guyatt et al., 1986)
// what this is, and isn't
This is the single-case experimental design (Barlow & Hersen, 1984) — the N-of-1 trial (Guyatt et al., 1986) — sized for one person's routine. The method is established; this page lays it out as a form. One variable at a time: change two things and neither can be credited.
The measure and the reversal rule are fixed before day 1 because after-the-fact judgment is biased — memory smooths, and wanting the change to work colors the read (kin: the introspection ceiling). A number written down each evening carries more than the recollection of how the week felt.
It designs experiments on routines — sleep, walks, screens, caffeine. It is a method template. This card is the plainest member of the family, an A-B design with a written reversal rule; a full N-of-1 trial adds randomization, washout, and repeated crossovers. The strongest objection is fair: an A-B run shows change but cannot fully separate the change from coincidence — a season, a workload, a cold. The reversal rule and the pre-set decide-by date are the guards this size allows. Medical or psychiatric changes belong with a clinician.
Kin: engineering therapy, the introspection ceiling, reframe. If what needs changing is heavier than a routine, that's worth real help — see dangers.