On Wed, 6 Aug 2008 17:37:38 -0400, Muthia Kachirayan <muthia.kachirayan@GMAIL.COM> wrote:

>On Wed, Aug 6, 2008 at 11:49 AM, sam <samygeb@gmail.com> wrote: > >> Hi all >> >> I am wrestling with this problem, I am sure some body could help me. I am >> posting the question again. I have a 24 hours blood pressure data with >> measurments taken every 20 minutes. The data looks some thing like this: I >> have more than 1000 subjects. >> >> ID SystBp Time >> 01 140 8:30 (starting time) >> 01 135 8:50 >> 01 136 9:10 >> . . . >> . . . >> . . . >> 01 135 8:30 (ending time- the next day) >> >> 02 137 9:30 (starting time) >> 02 125 9:50 >> . . . >> . . . >> . . . >> 02 135 9:30 (ending time- the next day) >> >> 03 122 14:50 (start time) >> 03 130 15:10 >> 03 134 15:30 >> . . . >> . . . >> . . . >> 03 137 15:50 (ending time- the next day) >> >> I want to derive variables 24 hour mean systbp, mean systbp every 3 hours >> and mean daytime systbp and nighttime bp in such away that the newly >> derived dataset is one observation pre subject. >> >> The desired output >> >> Id 24hmean systbp3 systbp6 systbp9... systbp24 daytimebp nighttimebp >> 01 127.5 130.5 . . . . . >> 02 135.8 125.6 . . . . . >> 03 140.9 124.7 . . . . . >> >> I tried to use arrays to solve the problem but I have no luck so far. >> >> Thank you >> sam >> > >Sam. > >How time variable is represented ? Do you use date and time together to >determine today's time to nextday's time? > >How do you define day-time and night-time ? > >How do you want the 3-hr duration to be handled - Is it every 3 hours from >the start time for each patient? Or do you want fixed intervals like, 8 - >11, 11 - 1, 1 - 3 etc ? > >Muthia Kachirayan

The first thing is to fix the time values so that they will sort and compare chronologically. Add 24:00 to each time value which occurs on the second day.