An important difference between the findings of a similar study
conducted in the US and the current investigation is the fact that,
unlike in this US, PM10 concentrations did not decline in Australia
during the period of investigation. This means that two potential
reasons given in the US study for a decline in the short-term effect
of PM10, related to a declining PM10 concentration, do not apply to
the current study. This means that in the current study we can rule these out as possible reasons for the observed decline in the shortterm
mortality effect of PM10. Importantly, this allows a “tighter
net” to be cast over the possible reasons for the decline observed in
our study.