According to a study by the University of Edinburgh and the UK Medical Research Council Plaid voters were thicker than their Lib Dem, Labour and Tory counterparts at the age of 10.
Some good news (at last) for the Liberal Democrats is that their voters were the brainiest kids from the main parties (only the Greens had brighter kids growing into voters). The Tories pipped Labour to third place with Plaid voters strolling in 5th, marginally ahead of their Scottish counterparts. UKIP and non-voters were low IQ children while, unsurprisingly, BNP voters were the least intelligent as children!
The "research" tested 6,000 UK kids aged 10 and then, 24 years later, asked them who they voted for in 2001.
Of course, if you believe such research has any bearing on reality then you're not even smarter than a ten year old kid who'll grow up to be a BNP voter!