[R-sig-ME] Interpretation of residual plot using DHARMA package for mixed model

[Tahsin Ferdous]

Dear all.

I am struggling to interpret the residual plots from the Dharma package. If
we find a red line in residual plot,does it mean there is
heteroscedasticity in the model for the predictor variables? If the solid
line matches with the dashed line, can we say there is no
heteroscedasticity? I have attached three residual plots here to understand
heteroscedasticity of the model.  In the first plot, quantile deviationare
detected by the red line, so there is heteroscedasticity in the model. This
is for the model which includes all covariates. Then I created the residual
plot for one by one covariate to know which predictors are responsible for
variable dispersion. The 2nd and 3rd plots are for just one predictor. In
the 2nd plot, three solid lines are red and there exhibits a clear
deviation from the dashed line. So, there is heteroscedasticity in the
model for that predictor. The 3rd plot is box plot.The distribution for
each factor level should be uniformly distributed, so the box should go
from 0.25 to 0.75, with the median line at 0.5 (within-group ). As the two
box plots are red and it shows deviation of median line from 0.5, so there
is heteroscedasticity in the model for the predictor. The 4th plot shows
less deviation. Can we say this is better? I need your expert suggestions
and also please refer me to any article where I find a clear explanation of
heteroscedasticity checking by residual plot using DHARMA.Many thanks.

Kindest regards,

Tahsin

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