There is still a difference between over-representation and bias. What you reference in your comment falls under what I call self-selection in the article. And I go on to cite work by Shields and Dunn affirming that this isn't due to any hostile environment for conservatives, but really is related more to their personal choices and values. That can hardly be reasonably called an institutional bias.

I also mention a couple surveys showing that conservative views on higher education have changed as recently as the last 3-4 years. There are questions to ask here, but I think they are more about how we understand our political values and what stance conservatives ought to take towards college if they want to see their representation increase at universities. Ironically, that would be more in keeping with their beliefs about personal responsibility, wouldn't it, rather than blaming higher education itself for being biased against them.