Description Usage Arguments Value Author(s) References See Also Examples
The difference index, D(x), for pairs is the simple arithmetic difference between one subpopulation's conditional equated score, y_j(x),and another subpopulation's conditional equated score, y_j'(x). Formally,
(y_j(x)-y_j'(x))/s,
where x is a score on the original (i.e., not equated) scale and s is the standard deviation of x scores in the (sub)population of interest. It is considered a pairwise, conditional invariance method. It was adapted by Huggins and Penfield (2012) from the analogous unconditional index, MD, presented by Kolen and Brennan (2004). It provides practitioners with the direction and magnitude of equated score differences between a pair of subpopulations at each level of the original scale.
1 | dx(x, g1, g2, d, s, ymax, xlab, color)
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x |
a column vector of scores on which the D(x) is conditioned |
g1 |
a column vector of equated scores based on a single subpopulation (aligned with elements in x) |
g2 |
a column vector of equated scores based on a different single subpopulation (aligned with elements in x) |
d |
a scalar of the positive difference that matters (negative of d will be applied as the negative difference that matters) |
s |
a scalar representing the standard deviation of x for any (sub)population of interest (e.g., synthetic population) (default is 1, which leads to calculation of the unstandardized D(x)) |
ymax |
A maximum value for the y axis of the plot (default = 3 + the maximum D(x) value)(negative of ymax will be applied to ymin of plot) |
xlab |
A label for the x axis of the plot (default = Score Scale) |
color |
color of D(x) line and points on plot (default = red) |
A data frame of D(x) indices, conditioned on the score scale
A plot of the D(x) indices in reference to the difference that matters
Anne Corinne Huggins-Manley
Huggins, A.C., & Penfield, R.D. (2012). An NCME instructional module on population invariance in linking and equating. Educational Measurement: Issues and Practices, 31, 27-40.
Kolen, M.J., & Brennan, R.L. (2004). Test equating, scaling, and linking: Methods and practices (2nd ed.). NY: Springer.
1 2 3 4 5 6 7 8 9 10 11 12 | #Unstandardized D(x) for subpopulation 1 and subpopulation 2 in the example data set, ex.data
dx(x=ex.data[,1],g1=ex.data[,3],g2=ex.data[,4],d=.5)
#Unstandardized D(x) for subpopulation 1 and subpopulation 2 in the example data set, ex.data,
#with adjustments to the maximum y-axis on the plot, a new xlabel, and points/line in blue.
dx(x=ex.data[,1],g1=ex.data[,3],g2=ex.data[,4],d=.5,ymax=2,xlab="AD(x)",color="blue")
#Unstandardized D(x) for subpopulation 4 and subpopulation 5 in the example data set, ex.data
dx(x=ex.data[,1],g1=ex.data[,6],g2=ex.data[,7],d=.5)
#Standardized D(x) for subpopulation 4 and subpopulation 5 in the example data set, ex.data
dx(x=ex.data[,1],g1=ex.data[,6],g2=ex.data[,7],d=.5,s=4.2)
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