Hi all - I have been looking on-line for an answer but cannot find one thus far, and was hoping anyone could be so kind to assist with some suggestions.
 
I have biological data of body size (y) over time (x), and after a preliminary inspection using a scatter plot the data suggest the body size is declining. I used a linear regression to confirm this, however, now I would like to examine what sort of underlying regression equation I can use to describe this decline, i.e., how do I get the parameters for the equation and for a more fitting curve (better than the loess)? I could not find anything online on this so far.
 
The curve is what I call a "reversed growth curve", and I also would like to examine at what year the decline is 5% or greater from the horizontal/asymptote (if that makes sense)......
 
 
 
 
 
thank you for any suggestions on this......m
 		 	   		  
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