plot.sdi: Plot Method for Objects of Class sdi
In SDT: Self-Determination Theory Measures

Description Usage Arguments Details Value Author(s) References See Also Examples

S3 method to plot objects of the class sdi.

1 2	## S3 method for class 'sdi' plot(x, minscore = 1, maxscore = 5, ...)

`x`	A required object of the class `sdi`, obtained from a call to the function `sdi`.
`minscore, maxscore`	Optional numerics, integer-valued, giving the minimum score (typically 1) or maximum score (typically 4, 5, or 7) used in the scale procedure, respectively. See also ‘Details’.
`...`	Further arguments to be passed are ignored in this function.

This plot method graphs the results obtained from calculating the original or adjusted SDI or RAI index. It produces a scatterplot of the confounded or adjusted external locus component values (y-axis) versus the confounded or adjusted internal locus component values (x-axis), respectively. In addition, for comparison, the reference line y = x (red full line) for visual inspection of the deviation of the two types of values and the admissible range (gray dashed lines) for the original or adjusted SDI or RAI index component values are plotted. Points with higher original or adjusted SDI or RAI overall index values are shown in darker gray tone.

To define and plot the admissible range, we do need the minscore and maxscore arguments, where minscore is the minimum score used in the scale procedure (typically 1), and maxscore is the maximum score used in the scale procedure (typically 4, 5, or 7). Note that translation with ‘- minscore’ and averaging are applied in the definitions of the components of the adjusted SDI or RAI index. The admissible range in the adjusted measure case is given by [0, maxscore - minscore], which yields [0, 4] for the default values. The admissible range in the original index case is the interval [(2 * minscore) + minscore, (2 * maxscore) + maxscore], that is, [3, 15] for the default values.

The function gray of the package grDevices is used to plot the points in the scatterplot at different gray levels determined by their respective original or adjusted SDI or RAI overall index values.

If the arguments x, minscore, and maxscore are of required types, plot.sdi produces the plot and invisibly returns NULL.

Ali Uenlue <ali.uenlue@icloud.com>

Uenlue, A. (2016) Adjusting potentially confounded scoring protocols for motivation aggregation in organismic integration theory: An exemplification with the relative autonomy or self-determination index. Frontiers in Educational Psychology, 7(272), 1–4. URL https://doi.org/10.3389/fpsyg.2016.00272.

The main function of the package, which creates objects of the class sdi: sdi for the original and adjusted SDI or RAI index. print.sdi, the S3 method for printing objects of the class sdi; summary.sdi, the S3 method for summarizing objects of the class sdi. See also SDT-package for general information about this package.

## attach dataset to search path (so a variable can be accessed by name)
attach(learning_motivation)

## adjusted index plot
plot(sdi(intrinsic, identified, introjected, external))

## original index plot
plot(sdi(intrinsic, identified, introjected, external, compute.adjusted = FALSE))