Objective: The number needed to treat (NNT) is an index for determining the number of patients who need to be treated in order to prevent the occurrence of an adverse event when a new treatment instead of the standard one is used.
Methods: The properties of NNT were examined by using the geometric distribution formula as the probability for preventing the occurrence of an adverse event in the NNT.
Results: When the NNT was enlarged infinitely, the probability for the prevention of an adverse event by NNT was found to be 63.2% (=1−e⁻¹), and the number of patients who needed to show adverse event prevention at the probability of 95% was about 3 times as that of the NNT (Rule of Three).
Conclusion: When the effect of new treatment needs to be evaluated based on NNT, one should take these properties of NNT into consideration.

The awareness of many residents on generic drugs has increased recently, which is also reflected in their increased consumption. Enlightenment activities for citizens have become an important tool to further promote the use of generic drugs. We performed a questionnaire survey and assessed residents’ consciousness after a lecture on generic drug usage in a people’s forum. We received responses from 105 of the recruited 127 participants. Most questionnaire respondents were from the age group of 70 years and comprised about half of the sample. The respondents having undefined will to the question about use of generic drugs was the most frequent. Only a few participants answered that they hoped getting generic drugs from a pharmacy or hospital. The concerns and future requests for generic drugs were the cost of medicine, validity, safety, and quality. The middle group by which the participants were classified into a positive group, a middle group and a negative group among question on usage and request of generic drugs, in its percentage each age groups, was most. Many respondents answered that generic drug use “should be spread” after the lecture. However, it was identified that the communication between doctor, pharmacist, and the patient on generic drug use is insufficient in the open question. Enlightenment activities for citizens will become necessary because half of the respondents expressed negative opinions on the use of generic drugs.