I have a set of tooth wear data (from a non-human species) in the form of ratios--- the ratios are the amount of dentine exposure divided by the areas of the chewing surface of the tooth. These ratios are not normally distributed. I am interested in comparing males and females in terms of their wear ratios as a function of age. So, I have plotted these ratios against the ages of the individuals, and males seem to have a steeper linear slope than do females-- that is, the males wear ratios appear to increase faster as a function of age than do the females' wear ratios. I would like to know the best way to statistically compare males and females in terms of their linear regression slopes but the data, as I say, are not normal. Googling a bit, it seemed that Theil regression might work, but I am not sure. What would you recommend and if you have a recommendation can you point me in the direction of some SAS code that would help? Many thanks!
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