inomsubjektdesign

Inomsubjektdesign, also known as within-subject design, is a research design in which the same participants take part in all experimental conditions. Each participant serves as their own control, which reduces between-subject variability and often increases statistical power. The approach is widely used in psychology, education, and user research, especially when sample sizes are limited.

Key features include exposure of every participant to all levels of the independent variable, counterbalanced presentation orders to minimize sequence effects, and careful scheduling to control for time-related factors. Common methods to manage order effects include full randomization of condition order or structured approaches such as Latin square designs. In some cases, a washout period is used between conditions.

Limitations include potential order, practice, or fatigue effects and carryover of the treatment from one condition to another. If the intervention has lasting effects, within-subject comparisons may be confounded. The design often requires longer testing sessions per participant and careful ethical considerations when tasks are demanding.

Data are typically analyzed with repeated measures techniques, such as repeated measures ANOVA or linear mixed models, which account for within-participant correlations. Assumptions such as sphericity may apply, and corrections like Greenhouse-Geisser may be used if violated.

Within-subject designs are contrasted with between-subject designs, where different groups experience different conditions. A related variant is the cross-over design, common in clinical trials, combining within-subject manipulation with consideration of carryover effects.