st: How to refer to different time periods when writing code

["Jessica Kopsic" <jkops@andrew.cmu.edu>]

Dear List Members,

I'm new to using Stata with panel data and time series. I'm trying to
create a variable that refers to different time periods.
For each day, I have two questions:
Did you eat an apple today? (yes/no)
Did you eat an orange yesterday? (yes/no)
Foe each individual for each day I would like to create a variable called
Fruit, that would tell how many pieces of fruit a person had each day. But
I'm stuck because orange is referring to the previous day. I do have a
variable identifying the time periods - "Day" with values  1, 2, 3, etc.
So if on Day 3 someone answered yes to the apple question and on Day 4
someone answered yes to the orange question, the value for Fruit for Day 3
would be 2.
I'm not certain how to tell Stata "the previous day" or "the next day"
when computing the variable.

Thank you, as always, for your excellent assistance!

Jessica

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/