# What causes bands/stripes in residual plots?

I ran a model and got the following residuals:

I proceeded to log the fitted values to get an idea of what's happening at the lower end of my predicted values:

It was then I saw on the left side the banded values. Their formation in stripes made me wonder what phenomenon could be producing this? Should I be adjusting my model somehow or just chalk this up to a quirk when logging fitted values?

These are from a negative binomial mixed effect model in R, if that helps.

• The fact that you have count data in your response is what causes that. The leftmost "stripe" in the bottom plot will almost certainly be the 0's, the next one the 1's, and so on. This is addressed in several questions on site. I'll try and find you some. – Glen_b -Reinstate Monica Dec 29 '15 at 3:49
• Here's one. A similar issue can be seen in multiple regression if you have a discrete response. – Glen_b -Reinstate Monica Dec 29 '15 at 5:10
• The easy way into this is to note that as residual $=$ observed $-$ fitted, particular observed values (0, 1, ....) define lines with negative unit slope and differing intercept. Your log scale for fitted warps them into curves. – Nick Cox Dec 29 '15 at 11:29
• (but with modifications for using Pearson residuals rather than raw residuals). – Nick Cox Dec 29 '15 at 12:31