There are a number of variables that can cause this. For example, we know that our context
(external environment and internal emotional states) can affect behaviour, so if your context
was significantly different when you completed an earlier test, then you might get a different
result. Also, some tests are more accurate than others, so if there was a difference in statistical
accuracy between two tests, then this could also lead to different results. In addition,
the natural process of maturing as you get older can cause changes as can actively participating
in personal development programmes.