Resources for Grouped Graphs
Swirl Lesson
Summary of many useful statistical terms
Quick overview of different variable types
Metadata describing the dataset used in this lesson
Weissgerber et al. 2019 paper from the journal Circulation (and the references cited within it) is a good overview of why it is recommended that you DO NOT use bar graphs for data with continuous dependent variables grouped by a categorical independent variable. This paper focuses on visualization problems in peripheral vascular disease journals, but the conclusions are widely applicable.
Webinar Report: Transforming data visualisation to improve transparency and reproducibility
This is a recording of a webinar talk given by Tracey Weissgerber that included many of the same concepts as the 2019 paper above.