In research fields such as computer science, academic publication mostly happens at two kinds of venues: peer-reviewed journals, and peer-reviewed conferences. The main difference is that conferences usually require that some author presents the work at the conference and pays a registration fee for the conference, whereas journals do not.
One criticism of conference in this light is that they are not open to all academics: they exclude researchers in poorer countries and institutions which cannot afford the conference registration fee or trip, they discourage geographically remote authors for which attending a conference is complicated, they discourage people who for personal reasons cannot easily travel (caring for a child or family member, having a disability, etc.).
My question is: has there been any systematic study to estimate the magnitude of this effect? E.g., take the dataset of article metadata for articles and journals of various fields, and study if there are systematic differences in terms of the author's institutions, countries, gender, etc.