An interesting journey of form UX, documented by Tim Paul. It started with browser defaults. It's unclear why that wasn't working. But interestingly, an alteration that included giant label-based click areas in color-offset boxes didn't help. What actually helped was bigger (and custom) radios and checkboxes.
So far they’ve tested really well. In research, people of all confidence levels are clicking these controls quickly and easily.
I used to think the size of SurveyMonkey radios was awkwardly large. Now I think it's probably a smart move.