st: Panel data: control if variable changes over time, for a given individual

["Giacomo PALLARO" <giacomo.pallaro@studenti.unipd.it>]

Dear Statalist,
I'm quite new to Stata and I have problems with a panel dataset for which I can't find a trivial solution (that I'm sure it exists). 
My unbalanced panel dataset contains an individual identifier, id (I've more than 150.000 obs so I can't do the job by hand), a wave identifier (from 1 to 4) and other variables among which mobirth (the month of birth of the interviewed individual).
mobirth is collected in each wave the individual participates but it happens that the guy gives different answers in different waves and I would like to check if this happens, so to be able to correct the data.
Unfortunately I don't know yet how to tell Stata to fix an individual and control if the mobirth is the same in all the waves the individual is present (recalling that an individual may not be present in all the waves, like the examples below).

       id            wave    mobirth
1140231201	1	    2
1140231201	2	    2
1140231201	3	    3
1140231201	4 	    2

1140234253	2	    5
1140234253	3	    6
1140234253	4	    6

1140232586	1	    3
1140232586	2	    4


Any answers would be greatly appreciated as I am really stuck!
Thank you!
Giacomo Pallaro