In the ** second step** the variables in these two working files were
used to divide each individuals into * pseudo-persons* according to
changes in category membership for the time-dependent covariates.
Each record in this file had an entry date and exit date for one of
the time-dependent strata and all additional information that was
needed by MAS for exact computation of person-years.
Table AIII shows that there were (3 x 3 x 10 = 90) possible
time dependent exposure categories. Note, however, that a person can
only move from lower to higher dose categories. The entry and exit
dates for the cumulative external dose groups were obtained by
interpolation within years after the appropriate lag had been
introduced. The entry and exit dates for internal exposure groups
were based on the mid-point of the year in which a category change
occurred. Workers employed at K-25 or TEC before they worked at X-10
or Y-12 entered follow-up in the ``Multiple'' facility category,
whereas individuals first hired at X-10 or Y-12 contributed
person-years to the facility of first hire until the end of the study
or until the date they became a multiple facility worker for the
appropriate lag. For the situation described in Table AIII,
and using a ten year lag, the 28,347 (note that 423 workers did not
have at least one year of follow-up and were excluded from the
analyses) workers are partitioned into 61,597 pseudo-individuals for
processing by MAS. A more detailed description of the exact
person-year stratification method is given in [1] Appendix
IV) and [8] who also discussed other
software that can be used for these computations.

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