Yes, the scale is absolute and not normalised. Each question asked respondents on their belief in a given conspiracy theory, and zero maps onto ‘neither believe nor disbelieve’. Since we asked six questions, the maximum possible score was a 12 (strongly agreeing with all the theories) or a -12 (strongly disagreeing with all the theories). For charting ease, we scaled the results by a factor of 12 to give absolute bounds of -1 and 1.
You are right, then, that the average across the whole sample is slightly below zero — but as the graph I included in my last post shows, supporters of Donald Trump do score above (and are statistically distinguishable from) zero. I think the right way to interpret the graph is that increasing conspiracy score is associated with increased support for Donald Trump.
All this is a first pass at a larger, compelling narrative. Professor Oliver’s forthcoming book, which I mention in the piece, gives many, many more analyses and charts that show the increasingly strong relationship between ‘magical thinking’ and political behaviour.