The changing criterion design.

Lewis et al. (1976) wrote the first how-to guide for the changing-criterion design.

They showed step-by-step graphs so you could copy the method in your own study.

No new treatment was tested; the paper only explains the design.

The authors proved you can track slow, stair-step behavior change with one person.

Each week you raise the target a little, and the line should climb with it.

If the data steps up with your new goals, the treatment is working.

Ferron et al. (2023) later added coin-flip randomization to the same design. You now decide ahead of time which days the goal will shift, so your stats are cleaner.

Levin et al. (2019) give a free Excel tool that works for any single-case study, including changing-criterion. You type in phases and the sheet randomizes them for you.

Manolov et al. (2022) built a free web plot that lets you check if the stair-step effect repeats in new participants.

Use this design when you want to shape behavior a little at a time—like adding one more math problem each day. Plot the steps on your graph, and if the data follow the steps, you have a clear effect. Pair it with the new random tools from Ferron et al. (2023) to make your study tougher and easier to publish.