I would like to style a layer where the fill of the symbols should be graduated e.g. based on an attribute showing the "proportion of the female population" and the size of the symbols based on another attribute e.g. "total population size".
In -> Layer Properties -> Symbology -> Graduated I can choose as a "method" either "size" or "color" (QGIS 3.2.2). However, I would need both.