It's a documented fact that along with a lower turnout of voters for elections in the Arab sector, mostly out of disgust for parties that follow their own agenda and seemingly couldn't care less about their own constituents, there is also a fair number of Arab voters who vote Meretz. Labor and other left-wing and centrist parties, some of whom have Arab candidates on their election lists. Given these facts, it's highly unlikely that even unified, there would be any significant increase in the number of seats the Arab parties hold.
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from the article: Rightists fear new election threshold will bring more Arabs to Knesset