In fact, nowadays researches are being done with repeated measures prior to design a randomized study.
It's called single-case experiment designs (SCED).
There are few papers you can refer to:
- Evaluating statistical and clinical significance of intervention effects in single-case experimental designs: An SPSS method to analyze univariate data.
- Sleepless in Sweden: A single subject study of effects of cognitive therapy for insomnia on three adolescents
-The Anxiety Severity Interview for Children and Adolescents: An individualized repeated measure of anxiety severity