You can set default answers for Radio and or Checkbox questions in DistillerSR. To do this, you must select the "Calculated Value" option in the Question Editor box.
var Default = 1;
if (Q2 != 2 && Q2 != 3 && Q2 != 4)
This function states that if the values 2, 3, or 4 are not selected, return the default variable of 1 (or "Yes") instead. In order for the function to work, you must take note of the calculation IDs for the questions on your Form, and use them in the function (in this example, the one question has an ID of Q2).
In the Answer Editor, the calculated values for your responses can be numbered as 1, 2, 3, and 4, respectively, as demonstrated below, and these values would be used in the function as well:
When previewing the Form, "Yes" is selected as the default answer because of the function: