Behavioral obesity research: Where have all the single subjects gone?

Bachman et al. (1988) looked at every behavioral obesity study they could find. They noticed most had switched from single-subject designs to big group trials. The paper asks a simple question: did this switch kill progress?

The review says yes. Group designs hide which clients actually lose weight. Without single-case data, clinicians can’t tell what works for whom. The field stopped learning, so treatments stayed stuck.

Frankot et al. (2024) answers the paper 36 years later. They say giant datasets can spot individual differences without going back to N=1. It’s not a fight—both want the same thing: know who responds.

Alfonsson et al. (2015) ran exactly the kind of group RCT the target paper critiques. Their mixed results show the problem: the trial says “no effect” even though some clients clearly improved.

Fernandez et al. (2023) sides with E et al. They show single-case methods still work—just in zoo welfare instead of weight loss. Same science, different animals.

If you treat obesity or eating issues, don’t trust group averages alone. Run one-client probes: graph weight daily, stagger treatments, look for clear jumps. One good ABAB chart beats a 50-person RCT for shaping your next clinical move.