This graph plots the residuals in the order of the corresponding observations. The plot is useful when the order of the observations may influence the results, which can occur when data are collected in a time sequence or in some other sequence, such as geographic area. This plot can be particularly helpful in a designed experiment in which the runs are not randomized.

The residuals in the plot should fluctuate in a random pattern around the center line. In orthogonal regression, residuals are correlated with each other. However, you can examine this plot to see if a correlation exists between residuals that are near each other, indicating that the order of observations may influence the results. Correlation among residuals may be signified by:

·    An ascending or descending trend in the residuals

·    Rapid changes in signs of adjacent residuals

For the glucose data, the residuals appear to be randomly scattered about zero. There is no evidence of order influence.