I had to standardize the scores of a variable because the items composing it were measured on different Likert-type scales (5, 6, 7 points). After this, I ran a correlation between this variable and other variables, with which theoretically it is supposed to correlate negatively. This yielded though a positive correlation. Correct me if I'm wrong, but is this result due to the score standardization? Thank you!
No, it can't be due to score standardization, unless the standardization somehow involved multiplying by a negative number. I can't see why standardization would involve that, but you never know!
More usually, the standardization would be something like:
$S = 7/5*A + 6/5*B + C$
as opposed to
$S = A + B + C$
these two S will correlate very highly with each other and in the same direction with some other variable.