as.weight {plink}R Documentation

Calibration Weights

Description

This function facilitates the creation of weights for a set of theta values for use in the function plink

Usage

as.weight(theta1 = NULL, weight1 = NULL, theta2 = NULL, weight2 = NULL, 
  normal.wt = FALSE)

Arguments

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.

Details

If no theta values are supplied, the values for theta1 and theta2 will be equal interval values ranging from -4 to 4 with an increment of 0.05. 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, the values for weight1 and weight2 will be equal to 1/n for n 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.

Value

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.

Note

When normal.wt equals TRUE, theta1 and theta2 are standardized to determine normal density weights

Author(s)

Jonathan Weeks weeksjp@gmail.com

References

Kolen, M. J., & Brennan, R. L. (2004) Test Equating, Scaling, and Linking. New York: Springer

See Also

plink

Examples

# Create a set of default theta values and weights
wt <- as.weight()

# Create weights for a set of random normal theta values
wt <- as.weight(rnorm(100))

# Create an object with equal interval theta values and normal density weights
wt <- as.weight(normal.wt=TRUE)

# Create an object with random normal theta values and normal density weights
wt <- as.weight(rnorm(100),normal.wt=TRUE)

[Package plink version 0.0-4 Index]