Difusing th eDisorder

Article in this months soldier around the Ross kemp prog, states 3-4% of military known to suffer PTSD.
Article in Independent on weekend on 5th of november quoting from Kings College London 7%.
Far be it from me to question a colonel, but which is right??
If we take the amount of discharges per year, then the figure represents a significant impact in any bodys book.
Just asking
Does the % represent those discharged as a result of PTSD or those who have been diagnosed before release or everyone who has been diagnosed before and after leaving? That would explain the discrepancy. IMHO the % of PTSD sufferers would be very high if all cases were taken into consideration. I know I've got it for one.