Calculate Cumulants Lognormal Response Time Distribution
Source:R/get_mean_var_3PLN.R
getMean3PLN.Rd
Calculate the first and second cumulants (i.e., mean and variance) of item response time distributions given item parameters of the three-parameter log-normal model (3PLN) for response times.
Value
a matrix with either the mean or the variance of the response time distributions,
with columns for different zeta
and rows for different items
Details
Calculate the first and second cumulant of the two-parameter log-normal (2PLN)
model for response times according to van der Linden (2006) or the 3PLN according
to Klein Entink et al. (2009). If the speed sensitivity parameter phi
in the 3PLN equals 1
, the model reduces to the 2PLN, yet with a
different parameterization for the item specific residual variance sdEpsi
compared to van der Linden (2006).
The cumulants are computed for one or more speed parameters, and for one or more sets of item parameters.
The calculation is based on Fenton (1960). For the model by van der Linden (2006), the calculation was first introduced by van der Linden (2011).
Functions
getMean3PLN()
: Calculate mean 3PLNgetMean2PLN()
: Calculate mean 2PLNgetVar3PLN()
: Calculate variance 3PLNgetVar2PLN()
: Calculate variance 2PLN
References
Fenton, L. (1960). The sum of log-normal probability distributions in scatter transmission systems. IRE Transactions on Communication Systems, 8, 57-67.
Klein Entink, R. H., Fox, J.-P., & van der Linden, W. J. (2009). A multivariate multilevel approach to the modeling of accuracy and speed of test takers. Psychometrika, 74(1), 21-48.
van der Linden, W. J. (2006). A lognormal model for response times on test items. Journal of Educational and Behavioral Statistics, 31(2), 181-204.
van der Linden, W. J. (2011). Test design and speededness. Journal of Educational Measurement, 48(1), 44-60.
Examples
# expected RT for a single item (van der Linden model)
getMean2PLN(lambda = 3.8, zeta = 0, sdEpsi = 0.3)
#> zeta=0
#> [1,] 46.75868
getVar2PLN(lambda = 3.8, zeta = 0, sdEpsi = 0.3)
#> zeta=0
#> [1,] 205.9003
# expected RT for multiple items (van der Linden model)
getMean2PLN(lambda = c(4.1, 3.8, 3.5), zeta = 0,
sdEpsi = c(0.3, 0.4, 0.2))
#> zeta=0
#> [1,] 63.11762
#> [2,] 48.42422
#> [3,] 33.78443
getVar2PLN(lambda = c(4.1, 3.8, 3.5), zeta = 0,
sdEpsi = c(0.3, 0.4, 0.2))
#> zeta=0
#> [1,] 375.17473
#> [2,] 406.86644
#> [3,] 46.58091
# expected RT for multiple items and multiple spped levels (Klein Entink model)
getMean3PLN(lambda = c(3.7, 4.1, 3.8), phi = c(1.1, 0.8, 0.5),
zeta = c(-1, 0, 1), sdEpsi = c(0.3, 0.4, 0.2))
#> zeta=-1 zeta=0 zeta=1
#> [1,] 127.10328 42.30901 14.08345
#> [2,] 145.47438 65.36585 29.37077
#> [3,] 75.18863 45.60421 27.66035
getVar3PLN(lambda = c(3.7, 4.1, 3.8), phi = c(1.1, 0.8, 0.5),
zeta = c(-1, 0, 1), sdEpsi = c(0.3, 0.4, 0.2))
#> zeta=-1 zeta=0 zeta=1
#> [1,] 1521.4086 168.57687 18.67885
#> [2,] 3671.9751 741.35899 149.67780
#> [3,] 230.7168 84.87596 31.22412