Few days back I took an IQ test (online mensa norway) and found my IQ score to be 85. I actually had my IQ professionally tested 16 months ago by a psychologist when I was 18, and found out that I am pretty average (I got a score of 101).
I know that online tests are not valid, possibly explaining the lower score of 85. Nonetheless, mensa seems OK,as they claim that their test was correlated with other standardized tests.
So my question is: can IQ within- test (i.e.., test / re-test scores) vary over periods of time (say months to a few years, or even from a day to day basis?), or are the differences observed here better explained by between-test variability?