seated balance measurement

Hi all,
I'm looking at performing a research project for my 3rd year dissertation looking at the effect on horse riding on balance on the assumption that regular horse riders have better seated balance than non riders, clinical implications are for hippotherapy with cerebral palsy patients.
does anyone have any information which might be useful to me, specifically, on seated balance measurement, hippotherapy as a treatment modality, or any useful ideas for my project ??
Any advice much appreciated :-)