I noticed that a common metrics for image quality assessment (Monte Carlo path tracing) is MSE between the generated image and a reference one. My question is: why isn't the standard deviation ever mentioned? Isn't it necessary? Shouldn't we generate n number of samples, compare them all with the reference, and then report the average and the standard deviation? This is how I have always seen results in technical papers, except for papers in Graphics. I am wondering if the fact that path tracing is unbiased plays a role in the missing std dev. Thank you.