Table 2.

The average engagement of a post is the number of reactions expected for a post and is a measure of how much a post is amplified in each social media platform.

	${\mathcal{E}}^U$	${\mathcal{E}}^R$	$\alpha$
Gab	5.6	1.4	3.9
Reddit	22.7	40.1	0.55
Twitter	15.1	15.6	0.97
YouTube	$1.4\times {10}^4$	$3.9\times {10}^4$	0.35

The average engagement ${\mathcal{E}}^U$ (for unreliable post) and ${\mathcal{E}}^R$ (for reliable post) vary from platform to platform, and are the largest in Twitter and the lowest in Gab. The coefficient of relative amplification $\alpha ={\mathcal{E}}^U/{\mathcal{E}}^R$ measures whether a social media amplifies more unreliable ($\alpha >1$) or reliable ($\alpha <1$) posts. Among more popular social media platforms, we notice that Twitter is the most neutral ($\alpha \sim 1\%$ i.e. ${\mathcal{E}}^U\sim {\mathcal{E}}^R$), while YouTube amplifies unreliable sources less ($\alpha \sim 4/10$). Among less popular social media platforms, Reddit reduces the impact of unreliable sources ($\alpha \sim 1/2$) while Gab strongly amplifies them ($\alpha \sim 4$).