title: Calculating deviation from line y=x of bivariate data
body: <p>As shown below, I have bivariate data, and in an ideal world, this data would fit the straight line (y=x).  In Python, how do I calculate the deviation of each point from that line (y=x)?  Is it possible to quantify the mean deviation from that straight line fit?  I'm just trying to think of a way to quantify how my data varies from a 1:1 ratio.  Any suggestions are appreciated.   I am working with data set up in a Pandas DataFrame. Thanks.</p>
  
  <p><a href="https://i.stack.imgur.com/1Bj22.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1Bj22.png" alt="enter image description here"></a></p>