This is of course an old chestnut and I have myself previously reported research on it. I found that LEFTISTS were dumber. So what are we to make of the latest research report below? Not much. Following a pattern that is all too common among psychologists, the author seems never to have heard of the concept of sampling. A group of college students or even college applicants is NOT representative of the population as a whole. And young people are notoriously Left-leaning. They have so little experience that they know no better. So if Left-leaning people among a Left-leaning group are smarter, it probably just means that smarter people are better able to pick up what is required for acceptance in that group. It has no wider implications than that.
Even if the results were generalizable, however, there would still be problems with the inferences to be drawn from them. There is in fact some generalizable evidence on the topic drawn from general population sampling. I discuss it here
Conservatism and cognitive ability
Conservatism and cognitive ability are negatively correlated. The evidence is based on 1254 community college students and 1600 foreign students seeking entry to United States' universities. At the individual level of analysis, conservatism scores correlate negatively with SAT, Vocabulary, and Analogy test scores. At the national level of analysis, conservatism scores correlate negatively with measures of education (e.g., gross enrollment at primary, secondary, and tertiary levels) and performance on mathematics and reading assessments from the PISA (Programme for International Student Assessment) project. They also correlate with components of the Failed States Index and several other measures of economic and political development of nations. Conservatism scores have higher correlations with economic and political measures than estimated IQ scores.