not only is the effect fairly modest (~30-40%) but there are countries (Germany) where the trend is absent or reversed, and reading the cited paper, to make the study feasible at all it's focused specifically on the amplification of tweets from elected politicians rather than ideology in general, which means that a comparatively small amount of organized traffic generation could sway the results substantially
in addition, in Canada the worst of the anti-left-wing bias is against the Liberal Party in particular, which many left-wing Canadians also detest for reasons that are peculiar to the Liberal Party
