# Goniometer data analysis

I am designing a health science experiment for uni and am focussing the study on measuring range of motion in a person's knee before and after they wear a copper bracelet. To measure the ROM, we are using a goniometer, which is a giant protractor with 2 arms that align with the angle of the joint to provide the degree of movement in that joint. This might sound basic, but I'm having a fight with myself as to whether this data is ordinal or ratio. I think it might be ratio because measurements are taken when the person is lying down (ie flat at 0 degrees), and you cant have a -ve degree, but it could be considered ordinal if you use the baseline measurement as an arbitrary '0 degree' point and then have + or - results from that point. Which way is the 'normal' way of using this data, because ultimately I just want to have 'before' and 'after' data to compare - please help!

• An aside: I would urge you to please be extremely careful with your study design. Involve a qualified statistician in the design before you collect any data. In goniometer studies in which I've been involved in the past (and only after data were collected), the single largest source of variation is the person taking the measurements and this variation appears to swamp all others in many cases. Cheers. Commented Oct 6, 2011 at 12:57