Regarding twitter, the population growed and changed composition over time too. For example pre and Post Oprah around 2009 and explosive growth until 2014 when

Regarding twitter, the population growed and changed composition over time too. For example pre and Post Oprah around 2009 and explosive growth until 2014 when it slowed somewhat. So even if it's not a good representative of the whole internet, it's not a good representative of itself when looked at over time. One would have to use the same cohort of users from each year with the assumption that their usage stayed the same.