psych (version 2.4.1)

bock: Bock and Liberman (1970) data set of 1000 observations of the LSAT

Description

An example data set used by McDonald (1999) as well as other discussions of Item Response Theory makes use of a data table on 10 items (two sets of 5) from the Law School Admissions Test (LSAT). Included in this data set is the original table as well as the reponses for 1000 subjects on the first set (Figure Classification) and second set (Debate).

Usage

data(bock)

Format

A data frame with 32 observations on the following 8 variables.

index

32 response patterns

Q1

Responses to item 1

Q2

Responses to item 2

Q3

Responses to item 3

Q4

Responses to item 4

Q5

Responses to item 5

Ob6

count of observations for the section 6 test

Ob7

count of observations for the section 7 test

Two other data sets are derived from the bock dataset. These are converted using the table2df function.

lsat6

reponses to 5 items for 1000 subjects on section 6

lsat7

reponses to 5 items for 1000 subjects on section 7

Details

The lsat6 data set is analyzed in the ltm package as well as by McDonald (1999). lsat7 is another 1000 subjects on part 7 of the LSAT. Both sets are described by Bock and Lieberman (1970). Both sets are useful examples of testing out IRT procedures and showing the use of tetrachoric correlations and item factor analysis using the irt.fa function.

References

R.P. McDonald. Test theory: A unified treatment. L. Erlbaum Associates, Mahwah, N.J., 1999.

Examples

data(bock)
responses <- table2df(bock.table[,2:6],count=bock.table[,7],
        labs= paste("lsat6.",1:5,sep=""))
describe(responses)
## maybe str(bock.table) ; plot(bock.table) ...