as.weight {plink} | R Documentation |
This function facilitates the creation of either a set of quadrature weights or
weights based on a set of theta values for use in the function
plink
as.weight(n=40, theta1 = NULL, weight1 = NULL, theta2 = NULL, weight2 = NULL, normal.wt = FALSE, ...)
n |
number of quadrature points to use |
theta1 |
vector of theta values for the set of TO item parameters
(i.e. the item parameters that will not be transformed) |
weight1 |
vector of weights corresponding to theta1 . They must
sum to one. |
theta2 |
vector of theta values for the set of FROM item parameters
(i.e. the item parameters that will be transformed) |
weight2 |
vector of weights corresponding to theta2 . They must
sum to one. |
normal.wt |
if TRUE and weight1 is NULL , the weights for
theta1 and theta2 will be computed to correspond to the
densities from a normal distribution. |
... |
further arguments passed to other methods |
If no theta values are supplied, n
normal quadrature points and weights will be
computed using the gauss.quad.prob
function from
the statmod
package. Additional arguments can be passed to this function to change
the distribution used to compute the quadrature weights.
If values are only supplied for theta1
, the values for theta2
will equal those of
theta1
. If values are supplied for theta1
and theta2
, the length
of the two vectors must be equal.
If no weights are supplied, and normal.wt
=FALSE, the values for weight1
and weight2
will be equal to 1/m for m theta values. If no weights are supplied,
and normal.wt
=TRUE, the values for weight1
and weight2
will be equal
to the normal densities corresponding to the theta values.
If values are only supplied for weight1
, the values for weight2
will equal
those of weight1
. If values are supplied for weight1
and/or weight2
,
the length of the vector(s) should be equal to the length of the theta vector(s). If values
are supplied for weight1
or weight2
, normal.wt
will be ignored.
See Kolen & Brennan (2004) for more information on calibration weights.
Returns a list of length two. The first list element is an n x 2 matrix of theta values
corresponding to theta1
and theta2
. The second list element is an
n x 2 matrix of weights corresponding to weight1
and weight2
.
When normal.wt
equals TRUE
, theta1
and theta2
are
standardized to determine normal density weights
Jonathan P. Weeks weeksjp@gmail.com
Kolen, M. J., & Brennan, R. L. (2004) Test Equating, Scaling, and Linking. New York: Springer
# Create a set of 40 (default) theta values and weights using quadrature wt <- as.weight() # Create a set of 20 theta values and weights using quadrature wt <- as.weight(20) # Create a set of 40 quadrature points and weights using a uniform distribution wt <- as.weight(dist="uniform") # Create weights for a set of random normal theta values wt <- as.weight(theta1=rnorm(100)) # Create an object with equal interval theta values and normal density weights wt <- as.weight(theta1=seq(-4,4,0.05), normal.wt=TRUE)