Study Population

The study population in this historical cohort study consisted of two separate dynamic cohorts. One cohort, the "Union Cohort", was assembled from the membership records of the Canterbury Marlborough Westland branch of the New Zealand Meat Workers and

Related Trades Union covering the period 1 969 to 1 998. The "Company Cohort" was assembled from historical employment records obtained from three individual meat processing plants, covering the period 1 98 1 to 1 998. These were the Alliance Lorneville, and the Richmond Takapau and Richmond Oringi sub-cohorts.

4.4.1 _{The Union Cohort}

The Union Cohort was based on the annual membership lists of the Canterbury

Marlborough Nelson West Coast Branch of the New Zealand Meat Workers and Related Trades Union for the years 1 969 to 1 998. This union represented all workers, apart from those employed in management or in the trades associated with maintenance of the plant and equipment, from all meat processing plants located in the South Island north of the Waitaki River.

These union membership records had been compiled annually, as members signed on at the beginning of each season, from the butts of union membership tickets filled in by hand and distributed by the union delegate for each distinct work area or department. The butts of completed union ticket books were collected by the union branch office, and used to compile a typed and bound annual membership list complete for every year since 1 9 1 6. Information contained in this record included surname, up to three initials of given

names, meat processing plant, and work area or department. In large departments this was further broken down into subgroups according to tasks, for example among the

slaughterboard employees separate classifications would be given to butchers, slaughtermen and slaughterhouse labourers.

Thus the union membership records contained a complete work history for each member for the period that they were employed in the industry. Electronic files containing these annual membership records were converted to Microsoft ACCESS, and merged to produce a file containing a total of 1 57, 238 records, which represented 34,88 7 unique individuals. This file was sorted electronically by surname and first initial in order to consolidate the entries into unique records for individual workers, detailing each

individual's work history, and a unique ID number was allocated to each. Further manual sorting and checking of this file was necessary to complete this consolidation, primarily where minor errors in spelling of names had prevented an electronic match. In these instances individuals were matched on criteria that included the similarity of names and/or initials, meat processing plant name, work department or type of job, and geographical location.

However, the union records did not include full names (only initial(s) and surname) or date of birth. These were obtained by linking the union file to records of membership of a national meat industry superannuation scheme, operated under the National Provident Fund, which had accepted new members from the time of its establishment in 1 973 until

1 992 when it was replaced by a competing Meat Industry Superannuation scheme. A file containing 1 7, 684 individual records of members of the meat processing industry scheme was provided by the scheme's administrators Jacques Martin Ltd, as at year-end 1 99 1

which was the date at which membership would have been at its peak. This file included full names, dates of birth, gender, residential address and contributing employer.

The final file assembled, where a clear match of surname and at least first initial was made between the superannuation and union membership files, thus contained the unique personal identifiers necessary for follow-up. This file also contained a full work and exposure history (by job title or work area, and by species slaughtered) for a total of 4,064 study subjects (or 1 2% of the 34,887 people on the union file). The period of eligibility for inclusion in this sub-cohort was from 1 974 to 1 99 1 , with work history records available for eligible study subjects from 1 969 to 1 998. Thus, this cohort

consisted of individuals who were members of the Canterbury Marlborough Nelson West Coast branch ofthe New Zealand Meat Workers Union, and were also members of a meat industry superannuation scheme. It does not, therefore, represent all union members, but rather just those who joined the superannuation scheme (which as noted above

represented only 1 2% of the union members). It would be likely to be more representative of individuals who regarded their employment in this industry as long term than of casual or short-term employees.

4.4.2 _{The Company Cohort}

The Company Cohort was based on three sub-cohorts of workers from specific freezing works. The first sub-cohort was assembled from copies of annual printouts of employee masterfiles from a single freezing works located in Lorneville (Alliance Lorneville) over

the period 1 986 to 1 998, which the company had provided each year to the site union branch for the purposes of reconciling union membership and fee deduction records. The Lomeville plant was built in 1 960, initially with six mutton chains and one beef chain, and now operates four mutton chains each on a double shift while the processing of beef ceased in 1 998. This plant employs up to 1 800 staff at the peak of the season. The records available were full personnel records, which contained full name and date of birth and a full work and exposure (by job title and/or work area and species) history. The paper records were photocopied then scanned and read into Microsoft ACCESS, with a manual check of the entire file undertaken subsequently to confirm the accuracy of the

conversion to electronic form. Particular care was necessary to check the accuracy of the conversion of numerals contained in dates of birth and job title codes. Once converted to electronic form these files were merged then sorted electronically by surname and first initial to consolidate entries into individual records with a work history. Additional electronic sorting used the employee number that had been assigned to each worker by the company payroll section, and also the Inland Revenue Department (lRD) tax number, supplemented this consolidation into unique records. A unique ID number was then allocated to each of the 3430 study subjects contained in the Lomeville file.

The second and third sub-cohorts were assembled from similar annual employee master files provided by the management of two separate freezing works, owned by the same company (Richmond Ltd) and located at Oringi and Takapau in southern Hawkes Bay. Both works process sheep exclusively. Annual printouts of masterfiles of employees at the end of each financial year were available from both plants, for the period 1 98 1 to

1 996 at Takapau and 1 987 to 1 998 at Oringi. The records available from these plants included the IRD tax numbers for each employee, which subsequently proved useful in the follow-up conducted to ascertain vital status of individuals not recorded as having

died. In addition to the sorting on surname and initial to consolidate the file into unique records, including work histories for individuals, both the IRD number and the unique pay number assigned to individuals at the time of first hire were used for sorting. The format of the printouts of personnel records meant that it was not feasible to simply scan records for conversion to electronic form. A Microsoft ACCESS file was set up for each plant, and data for every third or fourth year was entered manually. In order to compile the files for the intervening years, these records were then copied and amended manually by making the necessary deletions or additions to account for the roughly 1 0% annual labour turnover. On completion of the transcription of these records it was noted that for

1 , 1 79 of the Takapau sub-cohort records, and for 333 of the Oringi sub-cohort records, no date of birth had been recorded. The files of employees with missing dates of birth were manually checked against medical records by staff of the medical centres at both sites, and in this way an additional 1 000 dates of birth were added to the Takapau file and another 1 3 8 to the Oringi file. The final sub-cohort files contained 1 , 1 96 individuals from Oringi and 2,057 individuals from Takapau.

4.4.3 _{Combination of the cohorts}

In the initial analyses, the Union Cohort and the three company sub-cohorts were analysed separately. In subsequent analyses, the three company sub-cohorts were

combined into a single Company Cohort. When this was done a check was made for people who had worked in more than one plant, and their records were consolidated (to avoid counting workers and deaths more than once). This only involved 36 workers and two deaths. Similarly, in some analyses the Union and Company Cohorts were combined and their records were consolidated, but this only involved 24 workers and no deaths. The years of employment and of follow-up of the meat workers sub-cohorts are shown in

Table 4. 1 below.

Table 4.1 _{Years of employment and follow-up for the meat workers sub-cohorts}

Sub-cohort Union Lomeville Oringi Takapau N 4,064 3,430 1 , 1 96 2,057 Years of Years of 1 974 - 1 99 1 1 988 -2000 1 986 - 1 998 1 988 -2000 1 987 - 1 998 1 988 -2000 1 98 1 - 1 996 1 988 -2000

All cohorts were followed from 0 110 11 1 988. For the Union Cohort and for one of the company sub-cohorts (Takapau) follow-up could have included earlier years, but this was

not done so that follow-up could be standardised across the various cohorts and also

because of difficulties with electronic matching of deaths and cancer registrations in the earlier years. In particular, the National Minimum Dataset, which utilises National Health

Index (NHI) numbers to link and store deaths, cancer registrations and hospital

admissions in electronic form, is only complete from 1 988. In any case, the numbers of deaths prior to 0 110 1 1 1 988 were small (estimated as 20 in the Union Cohort, 1 0 in the

Takapau sub-cohort, and zero in the Lomeville and Oringi sub-cohorts).