Do you know of a reputed index that evaluates the social media usage by country. I am trying to compare different countries for a study. But I need a credible source to measure the usage of Social Media.
If you have access to Statista (https://www.statista.com) that is a good source. Also, Oxford University (https://ourworldindata.org) publish them, though it may not be in the exact form you may want.
I would consider this (https://www.smartinsights.com/social-media-marketing/social-media-strategy/new-global-social-media-research/) credible as well. He updates the stats very frequently. A good site to follow if you are interested in social media.