When I had my 1998 brain injury, after 6 months they tested my IQ and it was 42 or 47 points lower than when I had previously had it tested. This was after significant cognitive improvement, too! It scared the crap out of me and was the first piece of evidence that got me to look at how injured I really was. My doctors argued with me that I was "romanticizing" a high IQ for which I no longer had any proof, but two years later when I was STILL injured but had gone through some cognitive/visual therapy, my IQ score on the same type of test was 21 points higher. It took another few years to recover fully, but official IQ tests are expensive, so I never had a follow up one done once I regained all my reading, thinking and writing ability.
(I'd actually be interested to take a test now, as I have a feeling my IQ would be higher than it was pre-injury. In compensating for areas that no longer worked, I had to maximize other latent areas, and those improved parts never disappeared after recovery.)
Anyway, ... while I don't believe IQ tests show everything, in my experience, they do measure
something accurately. At the 20-point improvement mark, I was about 1/2way through my recovery (both time-wise and treatment-wise), and that was a measured regaining of nearly 1/2 the amount of cognition/abilities I had lost. The whole experience sure made me appreciate ALL of my brain, though! Sometimes you really don't know what you got until it's GONE.
