Hi Neema,,
90 degree appraisal is that system where only the person and appraiser is involved during the appraisal..
180 degree appraisal is where the person, Appraiser and his immediate superior is also included..
Whereas, 360 degree appraisal is what, everything is very clearly inform to the appraisee, in this system everybody remains same only inclusion of sub ordinates is more..
Hope it must have cleared ur queries a little bit..
Regards,
Amit Seth.