The pro-Republican bias is due to both clustering of Dem voters in urban areas & intentional efforts by Republicans to gerrymander. The 2016 presidential vote (where uncontested races are not an issue) shows Trump carried 63/99 districts despite barely winning popular vote.
https://twitter.com/bcburden/status/1070132906658541568Edited by MrBlueSky at 09:37:26 on 12/05/18