To calculate the minimum sample size needed to conduct a survey to verify the claim that 68% of young adults do not brush their teeth regularly.
The sample size for a proportion estimation is given by
where:
is the z-score of the confidence level and p is the proportion being tested.
Setting our confidence level to be 95%, then
= 1.96
Thus,
i.e. N <span>≥ 335.
</span>Setting our confidence level to be 90%, then
= 1.645
Thus,
i.e. N <span>≥ 236.
</span>
Setting our confidence level to be 99%, then
= 2.58
Thus,
i.e. N <span>≥ 335.</span>