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Plot the standard normal curve with your own score scales

Source: R/standard_normal_custom.R
standard_normal_custom.Rd

Draws the standard normal curve, marked at every standard deviation with the percentage of cases in each interval, with the scales you describe in a data frame lined up under it. A scale can be a row of labelled tick marks (like T scores), a row of coloured bands (like stanines), or both.

Usage

standard_normal_custom(scales = standard_normal_scales_data(), size = 3)

Arguments

scales

A data frame with one row per tick mark or band, and the columns:

scale

Name of the scale, shown at the left of its row. Rows are drawn from top to bottom in the order the names first appear.

z

Position on the z axis: where the tick mark goes, or where the band starts.

label

Text shown at the tick mark or inside the band.

z_end

Optional. Where the band ends on the z axis. Leave the column out, or use NA, for a tick mark.

colour

Optional. Fill colour of the band. Bands without a colour are coloured from light to dark along their row.

The default, standard_normal_scales_data(), holds the scales of standard_normal_scales.

size

Text size of all labels, in millimetres (ggplot2 text size). The default of 3 suits figures around 7 inches wide.

Value

A ggplot object. Print it to draw the chart, or save it with ggplot2::ggsave(). The chart keeps a fixed aspect ratio, and every scale you add makes it taller.

See also

standard_normal_scales_data, standard_normal_scales

Examples

standard_normal_custom()

# your own scales: tick marks for a test score and bands for performance levels
my_scales<-rbind(data.frame(scale="SCORE",z=-3:3,z_end=NA,label=seq(20,80,10)),
                 data.frame(scale="LEVEL",z=c(-4,-1,1),z_end=c(-1,1,4),label=c("Low","Average","High")))
standard_normal_custom(my_scales)

# start from the standard scales, drop the grades and add Wechsler scaled scores (mean 10, SD 3)
scales<-standard_normal_scales_data()
scales<-scales[scales$scale!="GRADE",]
scales<-rbind(scales,data.frame(scale="SCALED",z=-3:3,z_end=NA,label=seq(1,19,3),colour=NA))
standard_normal_custom(scales)