RPIQ function

Ratio of Performance to InterQuartile distance (RPIQ)

This function computes the Ratio of Performance to InterQuartile distance (RPIQ), which is defined as interquartile range of the observed values divided by the Root Mean Square Error or Prediction (RMSEP). The RPIQ takes both the prediction error and the variation of observed values into account, providing a metric of model validity that is more objective than the RMSEP and more easily comparable across model validation studies. The greater the RPIQ, the better the model's predictive capacity. In contrast to the Residual Prediction Deviation (RPD), the RPIQ makes no assumptions about the distribution of the observed values (since the RDP includes a standard deviation, it assumed normal distribution of the observed values).

RPIQ(predicted, observed, na.rm = FALSE)

Arguments

• predicted: a numeric vector containing predicted values.
• observed: a numeric vector of the same length as predicted containing observed values.
• na.rm: Boolean parameter indicating whether NA values should be removed before the analysis

Returns

numeric value of the RPIQ

Details

Interpretation of the RPIQ differs in the literature, with different thresholds used for judging model quality.

Examples

predicted<-c(1,2,3,4,5,6,7,8,9,10)
observed<-c(1.5,1.8,3.3,3.9,4.4,6,7.5,9,11,10)

RPD(predicted,observed)

References

Bellon-Maurel V, Fernandez-Ahumada E, Palagos B, Roger J-M, McBratney A, 2010. Critical review of chemometric indicators commonly used for assessing the quality of the prediction of soil attributes by NIR spectroscopy, In TrAC Trends in Analytical Chemistry 29(9), 1073-1081.

Author(s)

Eike Luedeling