Change polytomous items to dichotomous item format

Transforms a matrix of items into a new matrix where the select polytomous items have been converted into comparable dichotomous items with the same information.

Usage

poly2dich(data, which.items = 1:ncol(data), sep = "_cat.")

Arguments

data

an object of class data.frame or matrix

which.items

a vector indicating which items should be transformed into the dichotomous form. Default uses all input items

sep

character vector pattern to append to each item name in data

Value

Returns an integer matrix

References

Chalmers, R., P. (2012). mirt: A Multidimensional Item Response Theory Package for the R Environment. Journal of Statistical Software, 48(6), 1-29. doi:10.18637/jss.v048.i06

Author

Phil Chalmers rphilip.chalmers@gmail.com

Examples

# \donttest{
data(Science)

head(Science)
#>   Comfort Work Future Benefit
#> 1       4    4      3       2
#> 2       3    3      3       3
#> 3       3    2      2       3
#> 4       3    2      2       3
#> 5       3    4      4       1
#> 6       4    4      3       3
newScience <- poly2dich(Science)
head(newScience)
#>      Comfort_cat.1 Comfort_cat.2 Comfort_cat.3 Comfort_cat.4 Work_cat.1
#> [1,]             0             0             0             1          0
#> [2,]             0             0             1             0          0
#> [3,]             0             0             1             0          0
#> [4,]             0             0             1             0          0
#> [5,]             0             0             1             0          0
#> [6,]             0             0             0             1          0
#>      Work_cat.2 Work_cat.3 Work_cat.4 Future_cat.1 Future_cat.2 Future_cat.3
#> [1,]          0          0          1            0            0            1
#> [2,]          0          1          0            0            0            1
#> [3,]          1          0          0            0            1            0
#> [4,]          1          0          0            0            1            0
#> [5,]          0          0          1            0            0            0
#> [6,]          0          0          1            0            0            1
#>      Future_cat.4 Benefit_cat.1 Benefit_cat.2 Benefit_cat.3 Benefit_cat.4
#> [1,]            0             0             1             0             0
#> [2,]            0             0             0             1             0
#> [3,]            0             0             0             1             0
#> [4,]            0             0             0             1             0
#> [5,]            1             1             0             0             0
#> [6,]            0             0             0             1             0

newScience2 <- poly2dich(Science, which.items = 2)
head(newScience2)
#>   Comfort Work_cat.1 Work_cat.2 Work_cat.3 Work_cat.4 Future Benefit
#> 1       4          0          0          0          1      3       2
#> 2       3          0          0          1          0      3       3
#> 3       3          0          1          0          0      2       3
#> 4       3          0          1          0          0      2       3
#> 5       3          0          0          0          1      4       1
#> 6       4          0          0          0          1      3       3

# }