The findings of the present study are subject
to some limitations. The number of participants for
age groups by regions or by other factors might be
relatively small and account for the inability to
examine the association among these sub-groups.
The unavailability of reliable data representing
socioeconomic status such as annual income also
might pose some limitation to identify the high risk
group. Moreover, the sampling procedure at the
final stage for individual participants might not be
completely at random which might affect the
accuracy of the estimated prevalence to a certain
extent. However, the present study had its strength in
including several provinces in a region with a large
number of small clusters which could reduce the
effect of homogeneity within the cluster and made
the samples a sound representativeness of the
national level. The procedures in collection of data
were also well standardized.