Answer: The 2-month instrusction can be shortened to suit the interval being used. If the interval is shortened much below 2 months, this may slightly reduce scores on some problem items and scales. Low frequency behaviors may also be missed if the rating interval is too short. However, if reassessments are planned at intervals of less than 2 months, respondents should use the same shortened interval for the initial ratings as well for each follow-up rating. For example, if follow-up rataings are to be done after a 1-month interval, the initial rating should also be based on a 1-month period, so that the initial scores will not be higher than the follow-up scores merely because they span a longer rating period. To allow time for behavioral changes to stabilize and to become clearly evident, reassessment intervals should generally span at least a month.