cNORM (version 3.3.1)

plotDerivative: Plot first order derivative of regression model

Description

This function plots the scores obtained via the first order derivative of the regression model in dependence of the norm score.

Usage

plotDerivative(
  model,
  minAge = NULL,
  maxAge = NULL,
  minNorm = NULL,
  maxNorm = NULL,
  stepAge = NULL,
  stepNorm = NULL,
  order = 1
)

Value

A ggplot object representing the derivative of the regression function.

Arguments

model

The model from the bestModel function, a cnorm object.

minAge

Minimum age to start checking. If NULL, it's automatically determined from the model.

maxAge

Maximum age for checking. If NULL, it's automatically determined from the model.

minNorm

Lower end of the norm score range. If NULL, it's automatically determined from the model.

maxNorm

Upper end of the norm score range. If NULL, it's automatically determined from the model.

stepAge

Stepping parameter for the age check, usually 1 or 0.1; lower values indicate higher precision.

stepNorm

Stepping parameter for norm scores.

order

Degree of the derivative (default = 1).

Details

The results indicate the progression of the norm scores within each age group. The regression-based modeling approach relies on the assumption of a linear progression of the norm scores. Negative scores in the first order derivative indicate a violation of this assumption. Scores near zero are typical for bottom and ceiling effects in the raw data.

The regression models usually converge within the range of the original values. In case of vertical and horizontal extrapolation, with increasing distance to the original data, the risk of assumption violation increases as well.

See Also

checkConsistency, bestModel, derive

Other plot: plot.cnorm(), plot.cnormBetaBinomial(), plot.cnormBetaBinomial2(), plotDensity(), plotNorm(), plotNormCurves(), plotPercentileSeries(), plotPercentiles(), plotRaw(), plotSubset()

Examples

# For traditional continuous norming model
result <- cnorm(raw = elfe$raw, group = elfe$group)
plotDerivative(result, minAge=2, maxAge=5, stepAge=.2, minNorm=25, maxNorm=75, stepNorm=1)