Using variables across projects

I am creating a project with 6 separate units, each having 4 units.  Each of the units will be posted as an individual project on a wordpress site.   There are many variables in this project in each of the units and some variables are used in an earlier unit and referenced in a later unit. For example, in unit 1 the user is asked to list 3 of their favorite activities and in a later unit the data stored in that  variable is referenced when the user is exploring some personal characteristics.  My question is in regard to how variables store data and if they can be used across projects and referenced as I described.