plotNormCurves function

Plot norm curves

This function plots the norm curves based on the regression model. It supports both Taylor polynomial models and beta-binomial models.

plotNormCurves(
  model,
  normList = NULL,
  minAge = NULL,
  maxAge = NULL,
  step = 0.1,
  minRaw = NULL,
  maxRaw = NULL
)

Arguments

• model: The model from the bestModel function, a cnorm object, or a cnormBetaBinomial / cnormBetaBinomial2 object.
• normList: Vector with norm scores to display. If NULL, default values are used.
• minAge: Age to start with checking. If NULL, it's automatically determined from the model.
• maxAge: Upper end of the age check. If NULL, it's automatically determined from the model.
• step: Stepping parameter for the age check, usually 1 or 0.1; lower scores indicate higher precision.
• minRaw: Lower end of the raw score range, used for clipping implausible results. If NULL, it's automatically determined from the model.
• maxRaw: Upper end of the raw score range, used for clipping implausible results. If NULL, it's automatically determined from the model.

Returns

A ggplot object representing the norm curves.

Details

Please check the function for inconsistent curves: The different curves should not intersect. Violations of this assumption are a strong indication of violations of model assumptions in modeling the relationship between raw and norm scores.

Common reasons for inconsistencies include: 1. Vertical extrapolation: Choosing extreme norm scores (e.g., scores <= -3 or >= 3). 2. Horizontal extrapolation: Using the model scores outside the original dataset. 3. The data cannot be modeled with the current approach, or you need another power parameter (k) or R2 for the model.

Examples

## Not run:

# For Taylor continuous norming model
m <- cnorm(raw = ppvt$raw, group = ppvt$group)
plotNormCurves(m, minAge=2, maxAge=5)

# For beta-binomial model
bb_model <- cnorm.betabinomial(age = ppvt$age, score = ppvt$raw, n = 228)
plotNormCurves(bb_model)
## End(Not run)

See Also

checkConsistency, plotDerivative, plotPercentiles

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