- Create a Force.com Site. Details, including "Creating a Force.com Site"
- Modify your Site's "Public Access Settings"
- Check "Read" access to "Survey" and "Survey Question" object.
- Check "Read" and "Create" access for "Surveys Taken" and "Survey Question Responses"
- Add the Visualforce page, "Take Survey" to the list of enabled Visualforce pages.
- Complete "General Surveys" steps.
- Check "Read" access for "Contact" object.
- Check "Read" access for "Case" object.
- Private OWD for Case and Contact ? i. Create a public group and add the survey site user. i. Grant read access to case and contact to this group by creating 2 sharing rules Check this thread for further information.