The study was done 7 years ago but the data used was from a data base that was over the years from 1972-2004. Also measure of intelligence was based on a vocabulary test of 10 words.
They did attempt to adjust their finding according to covariates inclinding race (white black other), eductation , marital status and household income, and doing so cut the size of their effect by about 1/3. Best case scenario between the most strongly Republican vs the most strongly Democrat, a look at nearly 6000 respondents there is about a 1.26 pt IQ difference with statistical signifance 0.001<p<0.01.
To my eye as a trained statistician this means absolutely squat. Modeling and correcting for covariates is never perfect, and with this small an effect and this large a sample size, a slightly misspecified statistical model can make random result appear statically significant. Particularly since other measures of conservatives such as voting pattern and opinions on issues seem to trend in the opposite direction (opposition to Homosexuality has a strongly statistically significant negative effect on IQ according to the paper).
When you then add in the fact that the data comes from a span of years over which there has been demographic shifts, and what it means to be a Republican has radically changed, and has made no attempt to take time into account, I wouldn’t know how to interpret the results even if they were real. They seem to use their contradictory results to make some story about social vs economic Republicans, my guess it that any difference is due to the fact that the changes in social attitudes have markedly changed over the years, such that its really just a change in the measure of verbal intelligence over time (or else its just random garbage, still the most likely scenario)
If I were reviewing this paper I wouldn’t recommend publishing it, but then I don’t know about the editorial policies of the journal, and given some of the other articles published
Individual differences in preferences for cues to intelligence in the face
I’m not sure that there is a very high bar.