Hi Everyone, Input from each of you give me lot of help. I just find out I have to use consent_ date to determine if visit_date of month06, 12,18, and 24  are out of +/- 3 month range. I need your further help. Jag and stat@sas's way are more fit for me. here is the data: ID    B          visit_date   consent_date 46    SCREENING   27-Oct-08   27-Oct-08 46    MONTH06     23-Apr-09        . 46    NOVA        27-Oct-08        . 46    MONTH12     26-Oct-09        . 46    NOVA        23-Apr-09        . 46    NOVA        3-Dec-09         . 46    MONTH18     10-Jun-10        . 46    NOVA        6-Jan-11         . 46    MONTH24     6-Jan-11         . 53    SCREENING   19-Dec-08   22-Dec-08 53    MONTH06     25-Jun-09        . Here is the output I want: ID    B         visit_date     dif from consent_date     flag 46    SCREEN      27-Oct-08   0     46    MONTH06     23-Apr-09   6     46    FLOW        27-Oct-08   0     46    MONTH12     26-Oct-09   12    46    FLOW        23-Apr-09   6     46    FLOW        3-Dec-09    14    46    MONTH18     10-Jun-10   20    46    FLOW         6-Jan-11   27    46    MONTH24     6-Jan-11    27    53    SCREEN      19-Dec-08   0     53    MONTH06     26-Jan-09   1                        Below Thanks, Xinjian ... View more

when you compare screen and month06 for ID 46, visit_date is in the range +/- 3 month of month06. We should not call these above or below. That is why I ask some changes. Thanks, Xinjian ... View more

Hi Ksharp, I used your program to get  output below: 1 46 SCREENING 10/27/2008 flag 8 46 MONTH06 04/23/2009 ABOVE 15 46 MONTH12 10/26/2009 ABOVE 18 46 MONTH18 06/10/2010 ABOVE 20 46 MONTH24 01/06/2011 ABOVE 21 53 SCREENING 12/19/2008 28 53 MONTH06 06/25/2009 ABOVE 3 month, the flag should not show above. Should I make some changes for the program? Thanks, Xinjian ... View more

Hi Hima, Yes, just add a new available to show status of visit_date. ... View more

Dear All, Thanks so much for your efforts and kindness. I tried some programs, the results were not I expected. Here are the details of my project. I have 80 subjects to monitor lab examinations. Each subject have screen visit as baseline, then has  4 follow ups at 6, 12, 18, and 24 months. I will use month 6, 12, 18, and 24 to do survival analysis. The follow up visit date maybe before or after designed visit date (or called target date). So I want to find out If the real visit date is +/- 3 month of each month. Then I have to resign the follow up months. I would have a new variable to identify with visit date is out of the range target date. Here is my data: ID   B                  visit_date 46 SCREEN      10/27/2008 46 MONTH06    4/23/2009 46 FLOW          10/27/2008 46 MONTH12    10/26/2009 46 FLOW            4/23/2009 46 FLOW            12/3/2009 46 MONTH18     6/10/2010 46 FLOW            1/6/2011 46 MONTH24     1/6/2011 53 SCREEN       12/19/2008 53 MONTH06     1/26/2009 Thanks, ... View more

I got new version of SAS 9.4, and installed it successfully. Thanks for your kindness. ... View more