Zero weights for respondents can occur for two reasons.
The HILDA sample in Wave 1 excluded people living in institutions (such as hospitals and other healthcare institutions, military and police installations, correctional and penal institutions, convents and monasteries) and other non-private dwellings (such as hotels and motels).
As a result, the HILDA sample is not representative of people living in non-private dwellings.
People that move into these dwellings after Wave 1 are given zero cross-sectional weights and zero longitudinal weights for the balanced panel starting from the wave in which they began living in a non-private dwelling.
The HILDA sample also excluded people living in remote and sparsely populated areas. Some of these areas are excluded from the Australian Bureau of Statistics' population benchmarks, which are used in the weighting process.
For Releases 1 to 4, the benchmarks only excluded remote and sparsely populated areas in the Northern Territory. Following Release 4, however, the ABS revised the areas considered remote and sparsely populated to include very remote parts of New South Wales, Queensland, South Australia, Western Australia and the Northern Territory.
These areas are determined by the Remoteness Area classification and have a value greater than 10.53 in the Accessibility/Remoteness Index of Australia. As a result, from Release 5, a small number of sample members living in these areas are given zero cross-sectional weights and zero longitudinal weights.