userfriendlyscience (version 0.7.2)

testRetestCES: testRetestCES

Description

The testRetestCES function computes the test-retest Coefficient of Equivalence and Stability (Schmidt, Le & Ilies, 2003).

Usage

testRetestCES(dat = NULL, moments = NULL,
              testDat = NULL, retestDat = NULL,
              parallelTests = 'means',
              sortItems = FALSE, convertToNumeric = TRUE,
              digits=4)
parallelSubscales(dat, convertToNumeric = TRUE)

Arguments

dat

A dataframe. For testRetestCES, this dataframe must contain the items in the scale at both measurement moments. If no dataframe is specified, a dialogue will be launched to allow the user to select an SPSS datafile. If only one dataframe is specified, either the items have to be ordered chronologically (i.e. first all items for the first measurement, then all items for the second measurement), or the vector 'moments' has to be used to indicate, for each item, to which measurement moment it belongs. The number of columns in this dataframe MUST be even! Note that instead of providing this dataframe, the items of each measurement moment can be provided separately in testDat and retestDat as well.

moments

Used to indicate to which measurement moment each item in 'dat' belongs; should be a vector with the same length as dat has columns, and with two possible values (e.g. 1 and 2).

testDat, retestDat

Dataframes with the items for each measurement moment: note that the items have to be in the same order (unless sortItems is TRUE).

parallelTests

A vector indicating which items belong to which parallel test; like the moments vector, this should have two possible values (e.g. 1 and 2). Alternatively, it can be character value with 'means' or 'variances'; in this case, parallelSubscales will be used to create roughly parallel halves.

sortItems

If true, the columns (items) in each dataframe are ordered alphabetically before starting. This can be convenient to ensure that the order of the items at each measurement moment is the same.

convertToNumeric

When TRUE, the function will attempt to convert all vectors in the dataframes to numeric.

digits

Number of digits to print.

Value

An object with the input and several output variables. Most notably:

input

Input specified when calling the function

intermediate

Intermediate values and objects computed to get to the final results

output$testRetestCES

The value of the test-retest Coefficient of Equivalence and Stability.

Details

This function computes the test-retest Coefficient of Equivalence and Stability (CES) as described in Schmidt, Le & Ilies (2003). Note that this function only computes the test-retest CES for a scale that is administered twice and split into two parallel halves post-hoc (this procedure is explained on page 210, and the equations that are used, 16 and 17a are explained on page 212).

References

Schmidt, F. L., Le, H., & Ilies, R. (2003) Beyong Alpha: An Empirical Examination of the Effects of Different Sources of Measurement Error on Reliability Estimates for Measures of Individual-differences Constructs. Psychological Methods, 8(2), 206-224. doi:10.1037/1082-989X.8.x.206

Examples

# NOT RUN {
# }
# NOT RUN {
### This will prompt the user to select an SPSS file
testRetestCES();
# }
# NOT RUN {
### Load data from simulated dataset testRetestSimData (which
### satisfies essential tau-equivalence).
data(testRetestSimData);

### The first column is the true score, so it's excluded in this example.
exampleData <- testRetestSimData[, 2:ncol(testRetestSimData)];

### Compute test-retest alpha coefficient
testRetestCES(exampleData);

# }