Plotting functions for the psych package of class “psych"

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Description

Combines several plotting functions into one for objects of class “psych". This can be used to plot the results of fa, irt.fa, VSS, ICLUST, omega, factor.pa, or principal.

Usage

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## S3 method for class 'psych'
plot(x,labels=NULL,...)
## S3 method for class 'irt'
plot(x,xlab,ylab,main,D,type=c("ICC","IIC","test"),cut=.3,labels=NULL,
 keys=NULL, xlim,ylim,y2lab,lncol="black",...)
## S3 method for class 'poly'
plot(x,D,xlab,ylab,xlim,ylim,main,type=c("ICC","IIC","test"),cut=.3,labels,
     keys=NULL,y2lab,lncol="black",...)
## S3 method for class 'residuals'
plot(x,main,type=c("qq","chi","hist","cor"),std, bad=4,
     numbers=TRUE, upper=FALSE,diag=FALSE,...)

Arguments

x

The object to plot

labels

Variable labels

xlab

Label for the x axis – defaults to Latent Trait

ylab

Label for the y axis

xlim

The limits for the x axis

ylim

Specify the limits for the y axis

main

Main title for graph

type

"ICC" plots items, "IIC" plots item information, "test" plots test information, defaults to IIC.,"qq" does a quantile plot,"chi" plots chi square distributions,"hist" shows the histogram,"cor" does a corPlot of the residuals.

D

The discrimination parameter

cut

Only plot item responses with discrimiantion greater than cut

keys

Used in plotting irt results from irt.fa.

y2lab

ylab for test reliability, defaults to "reliability"

bad

label the most 1.. bad items in residuals

numbers

if using the cor option in plot residuals, show the numeric values

upper

if using the cor option in plot residuals, show the upper off diagonal values

diag

if using the cor option in plot residuals, show the diagonal values

std

Standardize the resduals?

lncol

The color of the lines in the IRT plots. Defaults to all being black, but it is possible to specify lncol as a vector of colors to be used.

...

other calls to plot

Details

Passes the appropriate values to plot. For plotting the results of irt.fa, there are three options: type = "IIC" (default) will plot the item characteristic respone function. type = "IIC" will plot the item information function, and type= "test" will plot the test information function.

Note that plotting an irt result will call either plot.irt or plot.poly depending upon the type of data that were used in the original irt.fa call.

These are calls to the generic plot function that are intercepted for objects of type "psych". More precise plotting control is available in the separate plot functions. plot may be used for psych objects returned from fa, irt.fa, ICLUST, omega, as well as principal

A "jiggle" parameter is available in the fa.plot function (called from plot.psych when the type is a factor or cluster. If jiggle=TRUE, then the points are jittered slightly (controlled by amount) before plotting. This option is useful when plotting items with identical factor loadings (e.g., when comparing hypothetical models).

Objects from irt.fa are plotted according to "type" (Item informations, item characteristics, or test information). In addition, plots for selected items may be done if using the keys matrix. Plots of irt information return three invisible objects, a summary of information for each item at levels of the trait, the average area under the curve (the average information) for each item as well as where the item is most informative.

If plotting multiple factor solutions in plot.poly, then main can be a vector of names, one for each factor. The default is to give main + the factor number.

It is also possible to create irt like plots based upon just a scoring key and item difficulties, or from a factor analysis and item difficulties. These are not true IRT type analyses, in that the parameters are not estimated from the data, but are rather indications of item location and discrimination for arbitrary sets of items. To do this, find irt.stats.like and then plot the results.

plot.residuals allows the user to graphically examine the residuals of models formed by fa, irt.fa, omega, as well as principal and display them in a number of ways. "qq" will show quantiles of standardized or unstandardized residuals, "chi" will show quantiles of the squared standardized or unstandardized residuals plotted against the expected chi square values, "hist" will draw the histogram of the raw or standardized residuals, and "cor" will show a corPlot of the residual correlations.

Value

Graphic output for factor analysis, cluster analysis and item response analysis.

Note

More precise plotting control is available in the separate plot functions.

Author(s)

William Revelle

See Also

VSS.plot and fa.plot, cluster.plot, fa, irt.fa, VSS, ICLUST, omega, or principal

Examples

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test.data <- Harman74.cor$cov
f4 <- fa(test.data,4)
plot(f4)
plot(resid(f4))
plot(resid(f4),main="Residuals from a 4 factor solution",qq=FALSE)
#not run
#data(bfi)
#e.irt <- irt.fa(bfi[11:15])  #just the extraversion items
#plot(e.irt)   #the information curves
#
ic <- iclust(test.data,3)   #shows hierarchical structure 
plot(ic)                    #plots loadings
#

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