For those of you working with spell-data (could be panel, but I am thinking more of event-history data), there is a great tool that you should be aware of. You can get it at SSC by typing the following command:
ssc install tsspell
What can it do for you? Well, as I said it puts a spell on your data. By giving the command
tsset id timevar
tsspell spellvar
You will have to define your dataset by the identificer (‘id’) and the time variable (‘timevar’). Then, the next command defines the spells based on one variable (‘spellvar’). Whenever it changes, a new spell for that person is started.
So you could consider it to be a hierarchical position, and the spells identifying the career of a worker going through hierarchies. A spell in this context will give the spell (duration) within that hierarchy. Even if multiple observations exist — because there is new information on wages, education, other functions within the hierarchy, etc — only a change in hierarchy will be counted as a new spell.
Great tool, if you work with that type of data install it and read the help-file which explains the details.