difMH: Mantel-Haenszel DIF method

In difR: Collection of Methods to Detect Dichotomous Differential Item Functioning (DIF)

Description

Performs DIF detection using Mantel-Haenszel method.

Usage

difMH(Data, group, focal.name , anchor = NULL, match = "score", MHstat = "MHChisq", 
  	correct = TRUE, exact = FALSE, alpha = 0.05, purify = FALSE, nrIter = 10, 
  	p.adjust.method = NULL, save.output = FALSE, output = c("out", "default")) 
## S3 method for class 'MH'
print(x, ...)
## S3 method for class 'MH'
plot(x, pch = 8, number = TRUE, col = "red", save.plot = FALSE, 
  	save.options = c("plot", "default", "pdf"), ...)
 

Arguments

Data	numeric: either the data matrix only, or the data matrix plus the vector of group membership. See Details.
group	numeric or character: either the vector of group membership or the column indicator (within data) of group membership. See Details.
focal.name	numeric or character indicating the level of group which corresponds to the focal group.
anchor	either NULL (default) or a vector of item names (or identifiers) to specify the anchor items. See Details.
match	specifies the type of matching criterion. Can be either "score" (default) to compute the test score, or any continuous or discrete variable with the same length as the number of rows of Data. See Details.
MHstat	character: specifies the DIF statistic to be used for DIF identification. Possible values are "MHChisq" (default) and "logOR". See Details .
correct	logical: should the continuity correction be used? (default is TRUE)
exact	logical: should an exact test be computed? (default is FALSE).
alpha	numeric: significance level (default is 0.05).
purify	logical: should the method be used iteratively to purify the set of anchor items? (default is FALSE).
nrIter	numeric: the maximal number of iterations in the item purification process (default is 10).
p.adjust.method	either NULL (default) or the acronym of the method for p-value adjustment for multiple comparisons. See Details.
save.output	logical: should the output be saved into a text file? (Default is FALSE).
output	character: a vector of two components. The first component is the name of the output file, the second component is either the file path or "default" (default value). See Details.
x	the result from a MH class object.
pch, col	type of usual pch and col graphical options.
number	logical: should the item number identification be printed (default is TRUE).
save.plot	logical: should the plot be saved into a separate file? (default is FALSE).
save.options	character: a vector of three components. The first component is the name of the output file, the second component is either the file path or "default" (default value), and the third component is the file extension, either "pdf" (default) or "jpeg". See Details.
...	other generic parameters for the plot or the print functions.

Details

The method of Mantel-Haenszel (1959) allows for detecting uniform differential item functioning without requiring an item response model approach.

The Data is a matrix whose rows correspond to the subjects and columns to the items. In addition, Data can hold the vector of group membership. If so, group indicates the column of Data which corresponds to the group membership, either by specifying its name or by giving the column number. Otherwise, group must be a vector of same length as nrow(Data).

Missing values are allowed for item responses (not for group membership) but must be coded as NA values. They are discarded from sum-score computation.

The vector of group membership must hold only two different values, either as numeric or character. The focal group is defined by the value of the argument focal.name.

The matching criterion can be either the test score or any other continuous or discrete variable to be passed in the mantelHaenszel function. This is specified by the match argument. By default, it takes the value "score" and the test score (i.e. raw score) is computed. The second option is to assign to match a vector of continuous or discrete numeric values, which acts as the matching criterion. Note that for consistency this vector should not belong to the Data matrix.

The DIF statistic is specified by the MHstat argument. By default, MHstat takes the value "MHChisq" and the Mantel-Haenszel chi-square statistic is used. The other optional value is "logOR", and the log odds-ratio statistic (that is, the log of alphaMH divided by the square root of varLambda) is used. See Penfield and Camilli (2007), Philips and Holland (1987) and mantelHaenszel help file.

By default, the asymptotic Mantel-Haenszel statistic is computed. However, the exact statistics and related P-values can be obtained by specifying the logical argument exact to TRUE. See Agresti (1990, 1992) for further details about exact inference.

The threshold (or cut-score) for classifying items as DIF depends on the DIF statistic. With the Mantel-Haenszel chi-squared statistic (MHstat=="MHChisq"), it is computed as the quantile of the chi-square distribution with lower-tail probability of one minus alpha and with one degree of freedom. With the log odds-ratio statistic (MHstat=="logOR"), it is computed as the quantile of the standard normal distribution with lower-tail probability of 1-alpha/2. With exact inference, it is simply the alpha level since exact P-values are returned.

By default, the continuity correction factor -0.5 is used (Holland and Thayer, 1988). One can nevertheless remove it by specifying correct=FALSE.

In addition, the Mantel-Haenszel estimates of the common odds ratios α_{MH} are used to measure the effect sizes of the items. These are obtained by Δ_{MH} = -2.35 \log α_{MH} (Holland and Thayer, 1985). According to the ETS delta scale, the effect size of an item is classified as negligible if |Δ_{MH}| ≤q 1, moderate if 1 ≤q |Δ_{MH}| ≤q 1.5, and large if |Δ_{MH}| ≥q 1.5. The values of the effect sizes, together with the ETS classification, are printed with the output. Note that this is returned only for asymptotic tests, i.e. when exact is FALSE.

Item purification can be performed by setting purify to TRUE. Purification works as follows: if at least one item was detected as functioning differently at some step of the process, then the data set of the next step consists in all items that are currently anchor (DIF free) items, plus the tested item (if necessary). The process stops when either two successive applications of the method yield the same classifications of the items (Clauser and Mazor, 1998), or when nrIter iterations are run without obtaining two successive identical classifications. In the latter case a warning message is printed.

Adjustment for multiple comparisons is possible with the argument p.adjust.method. The latter must be an acronym of one of the available adjustment methods of the p.adjust function. According to Kim and Oshima (2013), Holm and Benjamini-Hochberg adjustments (set respectively by "Holm" and "BH") perform best for DIF purposes. See p.adjust function for further details. Note that item purification is performed on original statistics and p-values; in case of adjustment for multiple comparisons this is performed after item purification.

A pre-specified set of anchor items can be provided through the anchor argument. It must be a vector of either item names (which must match exactly the column names of Data argument) or integer values (specifying the column numbers for item identification). In case anchor items are provided, they are used to compute the test score (matching criterion), including also the tested item. None of the anchor items are tested for DIF: the output separates anchor items and tested items and DIF results are returned only for the latter. Note also that item purification is not activated when anchor items are provided (even if purify is set to TRUE). By default it is NULL so that no anchor item is specified.

The output of the difMH, as displayed by the print.MH function, can be stored in a text file provided that save.output is set to TRUE (the default value FALSE does not execute the storage). In this case, the name of the text file must be given as a character string into the first component of the output argument (default name is "out"), and the path for saving the text file can be given through the second component of output. The default value is "default", meaning that the file will be saved in the current working directory. Any other path can be specified as a character string: see the Examples section for an illustration.

The plot.MH function displays the DIF statistics in a plot, with each item on the X axis. The type of point and the color are fixed by the usual pch and col arguments. Option number permits to display the item numbers instead. Also, the plot can be stored in a figure file, either in PDF or JPEG format. Fixing save.plot to TRUE allows this process. The figure is defined through the components of save.options. The first two components perform similarly as those of the output argument. The third component is the figure format, with allowed values "pdf" (default) for PDF file and "jpeg" for JPEG file. Note that no plot is returned for exact inference.

Value

A list of class "MH" with the following arguments:

MH	the values of the Mantel-Haenszel DIF statistics (either exact or asymptotic).
p.value	the p-values for the Mantel-Haenszel statistics (either exact or asymptotic).
alphaMH	the values of the mantel-Haenszel estimates of common odds ratios. Returned only if exact is FALSE.
varLambda	the values of the variances of the log odds-ratio statistics. Returned only if exact is FALSE.
MHstat	the value of the MHstat argument. Returned only if exact is FALSE.
alpha	the value of alpha argument.
thr	the threshold (cut-score) for DIF detection. Returned only if exact is FALSE.
DIFitems	either the column indicators of the items which were detected as DIF items, or "No DIF item detected".
correct	the value of correct option.
exact	the value of exact option.
match	a character string, either "score" or "matching variable" depending on the match argument.
p.adjust.method	the value of the p.adjust.method argument.
adjusted.p	either NULL or the vector of adjusted p-values for multiple comparisons.
purification	the value of purify option.
nrPur	the number of iterations in the item purification process. Returned only if purify is TRUE.
difPur	a binary matrix with one row per iteration in the item purification process and one column per item. Zeros and ones in the i-th row refer to items which were classified respectively as non-DIF and DIF items at the (i-1)-th step. The first row corresponds to the initial classification of the items. Returned only if purify is TRUE.
convergence	logical indicating whether the iterative item purification process stopped before the maximal number nrIter of allowed iterations. Returned only if purify is TRUE.
names	the names of the items.
anchor.names	the value of the anchor argument.
save.output	the value of the save.output argument.
output	the value of the output argument.

Author(s)

Sebastien Beland
Collectif pour le Developpement et les Applications en Mesure et Evaluation (Cdame)
Universite du Quebec a Montreal
[e-mail], http://www.cdame.uqam.ca/
David Magis
Department of Psychology, University of Liege
Research Group of Quantitative Psychology and Individual Differences, KU Leuven
[e-mail], http://ppw.kuleuven.be/okp/home/
Gilles Raiche
Collectif pour le Developpement et les Applications en Mesure et Evaluation (Cdame)
Universite du Quebec a Montreal
[e-mail], http://www.cdame.uqam.ca/

References

Agresti, A. (1990). Categorical data analysis. New York: Wiley.

Agresti, A. (1992). A survey of exact inference for contingency tables. Statistical Science, 7, 131-177. doi: 10.1214/ss/1177011454

Holland, P. W. and Thayer, D. T. (1985). An alternative definition of the ETS delta scale of item difficulty. Research Report RR-85-43. Princeton, NJ: Educational Testing Service.

Holland, P. W. and Thayer, D. T. (1988). Differential item performance and the Mantel-Haenszel procedure. In H. Wainer and H. I. Braun (Ed.), Test validity. Hillsdale, NJ: Lawrence Erlbaum Associates.

Kim, J., and Oshima, T. C. (2013). Effect of multiple testing adjustment in differential item functioning detection. Educational and Psychological Measurement, 73, 458–470. doi: 10.1177/0013164412467033

Magis, D., Beland, S., Tuerlinckx, F. and De Boeck, P. (2010). A general framework and an R package for the detection of dichotomous differential item functioning. Behavior Research Methods, 42, 847-862. doi: 10.3758/BRM.42.3.847

Mantel, N. and Haenszel, W. (1959). Statistical aspects of the analysis of data from retrospective studies of disease. Journal of the National Cancer Institute, 22, 719-748.

Penfield, R. D., and Camilli, G. (2007). Differential item functioning and item bias. In C. R. Rao and S. Sinharray (Eds.), Handbook of Statistics 26: Psychometrics (pp. 125-167). Amsterdam, The Netherlands: Elsevier.

Philips, A., and Holland, P. W. (1987). Estimators of the Mantel-Haenszel log odds-ratio estimate. Biometrics, 43, 425-431. doi: 10.2307/2531824

Raju, N. S., Bode, R. K. and Larsen, V. S. (1989). An empirical assessment of the Mantel-Haenszel statistic to detect differential item functioning. Applied Measurement in Education, 2, 1-13. doi: 10.1207/s15324818ame0201_1

Uttaro, T. and Millsap, R. E. (1994). Factors influencing the Mantel-Haenszel procedure in the detection of differential item functioning. Applied Psychological Measurement, 18, 15-25. doi: 10.1177/014662169401800102

See Also

mantelHaenszel, dichoDif, p.adjust

Examples

## Not run: 

 # Loading of the verbal data
 data(verbal)

 # Excluding the "Anger" variable
 verbal <- verbal[colnames(verbal) != "Anger"]

 # Three equivalent settings of the data matrix and the group membership
 r <- difMH(verbal, group = 25, focal.name = 1)
 difMH(verbal, group = "Gender", focal.name = 1)
 difMH(verbal[,1:24], group = verbal[,25], focal.name = 1)

 # With log odds-ratio statistic
 r2 <- difMH(verbal, group = 25, focal.name = 1, MHstat = "logOR")

 # With exact inference
 difMH(verbal, group = 25, focal.name = 1, exact = TRUE)

# Multiple comparisons adjustment using Benjamini-Hochberg method
 difMH(verbal, group = 25, focal.name = 1, p.adjust.method = "BH")

 # With item purification
 difMH(verbal, group = "Gender", focal.name = 1, purify = TRUE)
 difMH(verbal, group = "Gender", focal.name = 1, purify = TRUE, nrIter = 5)

 # Without continuity correction and with 0.01 significance level
 difMH(verbal, group = "Gender", focal.name = 1, alpha = 0.01, correct = FALSE)

 # With items 1 to 5 set as anchor items
 difMH(verbal, group = "Gender", focal.name = 1, anchor = 1:5)
 difMH(verbal, group = "Gender", focal.name = 1, anchor = 1:5, purify = TRUE)

 # Saving the output into the "MHresults.txt" file (and default path)
 r <- difMH(verbal, group = 25, focal.name = 1, save.output = TRUE, 
            output = c("MHresults","default"))

 # Graphical devices
 plot(r)
 plot(r2)

 # Plotting results and saving it in a PDF figure
 plot(r, save.plot = TRUE, save.options = c("plot", "default", "pdf"))

 # Changing the path, JPEG figure
 path <- "c:/Program Files/"
 plot(r, save.plot = TRUE, save.options = c("plot", path, "jpeg"))

## End(Not run)
 

difR documentation built on July 2, 2020, 3:34 a.m.