Please forgive my ignorance, but I need to measure days between two dates on different observations of the same individual. Perhaps an example of my data would be helpful:   ID#     VAR1         VAR2     VAR1dummy     DATE 1           .                 X                0              30April2015 1      9May2015        .               1               31May2015 1          .                   .                0              30June2015 2          .                  X                0               30April2015 2          .                   .                0               31May2015 2    28June2015      .                1               30June2015 3      3April2015       .                1              30April2015 3          .                   .                0               31May2015 3          .                  X                0               30June2015   In the example above, I am attempting to measure the days between when Var1 has a date and when Var2 has a value of 'X' for each individual ID# (I created a dummy variable for when VAR1 has a date). For example, ID#1 has 9 days between when VAR1 appears and when VAR2 has an 'X', ID#2 has 59 and ID#3 has 88 Any help would be much appreciated!   Thanks ... View more