The four-in-one residual plot displays four different residual plots together in one graph window. This layout can be useful for comparing the plots to determine whether your model meets the assumptions of the analysis. The following residual plots are included in the graph:

·    Histogram: Indicates whether the data are skewed or outliers exist in the data.

·    Normal probability plot: Indicates whether the data are normally distributed, other variables are influencing the response, or outliers exist in the data.

If batch is a random factor, and the final model includes the batch by time interaction, then the variance of the marginal residuals depends on the time variable and may not be constant. You can use the conditional residuals to check the normality of the error term in the model.

·    Residuals versus fitted values: Indicates whether the variance is constant, a nonlinear relationship exists, or outliers exist in the data.

·    Residuals versus order of the data: Indicates whether there are systematic effects in the data due to time or data collection order.

To view the interpretation of each residual plot in the four-in-one plot, refer to the individual topic for each residual plot preceding this topic.