# Does my residuals vs fitted values plot show constant variance for my regression?

I'm having trouble interpreting my R output. I know when checking for variance no patterns should occur but I have only covered the textbook scenario where it is very easy to interpret. However with my output I was just wondering does the validated of constant variance hold up?

• I've tried giving a clearer title - I suspect that you mean "assumption" instead of "validated" in the final line? – Silverfish May 10 '16 at 18:44

It is difficult to judge a plot with such few data points. You could try a formal test of heteroscedasticity such as the Breusch-Pagan test, implemented in the ncvTest function of the car package. Given how small your data set is, I would be surprised if significant heteroscedasticity is found.
• I think you would be safe saying that it is difficult to tell based on such few data points, but there is perhaps a slight suggestion of non-linearity (U-shaped pattern). Something like this could happen if your response variable grows exponentially but you try to model it with a linear model, e.g., plot(lm(1.3^(1:8)~c(1:8)), which=1) – Slow loris May 10 '16 at 20:08