IN = individual responses recorded as vectors in the data file (one line represents one individual's responses to items 1 through k)
RA = marginal maximum likelihood is used for parameter estimation because we do not know where the items lie on the theta continoum
NI = number of items, k
NE = number of examinees
NCHAR = number of characters in the ID field for each respondent
NG = numbers of groups (for our discussion, we will only be dealing with a single group at a time)