I am trying to generate a count of how many total visits there were in a specific time period using the start date as a reference. There are 400+ observations and 100 visits.    Study design: On the start date, participants were expected to return to the clinic at 12 months ± 3 months, 24 months ± 3 months, and 36 months ± 3 months.    Data: (example) ID       Startdate        visit1                 visit2                visit3     ...        visit100 123    12MAR2009    13MAR2010     2AUG2010      4JUN2012       5DEC2015  456    14MAR2009    16MAR2010     4AUG2010      5JUN2012       10DEC2015  789    16MAR2009    19MAR2010     6AUG2010      6JUN2012       15DEC2015    What I need to know is if a patient has a visit within the range of: 9-15 months from the start date for 12 month visit and 21-27 months from the start date for 24 month visit and 33-39 months from the start date for 36 month visit   Using the attached set, this is an example of what the reporting table would look like… 12 month visits 29* 24 month visits 18 36 month visits 10 *This means that there were 29 visits that occurred between 9-15 months from the start date. ... View more