Who says you can’t quantify public deliberation? It is true that quantitative measurement hasn’t been a strong suit of the field. It is also true that some of the most significant impacts, such as policy changes, are inherently difficult to quantify. But at this point, enough scholarly research and evaluative work has been done that is possible to pull together a concise statistical glimpse of the kinds of things these projects accomplish. The DDC fact sheet "Deliberation by the Numbers" is available on the DDC resource page.