The numbers of matched pairs were 76, 16 and 12
from each of the three participating hospitals. Three-
fourths of participants were aged 55 or more, with more
males than females (Table 1). Primary school was the
highest education level for most participants in both case
and control subjects. There was an inverse association
between level of education and risk of oral cancer (P for
trend=0.001). Moreover, most participants were farmers
and had less than 5,000 Thai Baht (~160 USD) household
income per month, but inverse for control subjects who
had high (10,001 Baht or more) household income per
month, as shown in Table 1.