skilled migrants and business investors.<sup>6</sup> Specifically, any Tongan citizens aged between 18 and 45, who meet certain English, health and character requirements,<sup>7</sup> can register to migrate to New Zealand.<sup>8</sup> Many more applications are received than the quota allows, so a ballot is used by the New Zealand Department of Labour (DoL) to randomly select from amongst the registrations. Once their ballot is selected in the lottery, applicants must then provide a valid job offer in New Zealand within six months in order to have their application to migrate approved and be allowed to migrate.

The survey design and enumeration, which was overseen by the authors in the first half of 2005, covered random samples of four groups: (i) Tongan migrants to New Zealand, who were successful participants in the 2002/03 and 2003/04 PAC lotteries, (ii) successful participants from the same lotteries who were still in Tonga, either because their application for New Zealand residence was not approved (typically because of lack of a suitable job offer) or was still being processed, (iii) unsuccessful participants from the same lotteries who were still in Tonga, and (iv) a group of non-applicants in Tonga.<sup>9</sup>

> 6 The Pacific Access Category also provides quotas for 75 citizens from Kiribati, 75 citizens from Tuvalu, and 250 citizens from Fiji to migrate to New Zealand.

> 7 Data supplied by the DoL for residence decisions made between November 2002 and October 2004 reveals that out of 98 applications, only 1 was rejected for failure to meet the English requirement, and only 3 others were rejected for failing other requirements of the policy.

> 8 The person who registers is a Principal Applicant. If they are successful, their immediate family (spouse and children under age 18) can also apply to migrate as Secondary Applicants. The quota of 250 applies to the total of Primary and Secondary Applicants, and corresponds to about 70 migrant households.

9 The initial sample frame for groups (i) and (ii) was a list of the names and addresses of the 278 (out of almost 3000 applicants) successful participants in the 2002/03 and 2003/04 migration lotteries, which was supplied under a contractual arrangement with the New Zealand Department of Labour, with strict procedures used to maintain the confidentiality of participants. Approximately 100 of these successful ballots had been approved for residence in New Zealand by the time of the survey, although some of those families had not yet moved to New Zealand. We managed to locate 65 of the families that had migrated, giving a sampling rate of over 70 percent, and drew a random sample of 55 of the successful ballots that had not yet migrated. This non-migrant group includes those whose applications were rejected and those whose applications were still being processed. We use the actual number of accepted and rejected applications to weight our sample. The initial sample frame for the unsuccessful ballots (group (iii)) was a list of names and addresses provided by the DoL. We derived a sample of 78 unsuccessful ballots from this information, implicitly stratifying by island and by the village of residence when the applicant entered the ballot. The sample of non-applicants was obtained by selecting 60 households, with at least one member aged 18 to 45, in either the same villages that the migrants had been living in prior to migrating or in the same villages that unsuccessful ballots were found in. The interviewer for all the migrant households in New Zealand also interviewed about one-half of the households from the three samples in Tonga, reducing one potential source of extraneous variation between the samples. Interviewer effects on the mental health scores are discussed below.

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