Baseline lung function in the reference group was lower than expected based on the predicted values. This may be because the reference group was also exposed to significant levels of dust (table 1), or the fact that a significant proportion were Polynesians, who are known to exhibit lower lung function than Caucasians (see above). Also, the predicted values were based on a US population [18], which may not reliably predict lung function in New Zealanders. In any case, consistent associations were found, which were highly comparable with the results based on the measured lung function, indicating that the reported results are valid.