Checkbox sets are based on a list. I have a sample app that show how to setup a button to add items to a checkbox set on the fly and which items have and have not been selected. You don't have to have a button included in your app. This sample was created to show some options available with checkboxes. You would have a different record for each patient.
If you are trying to show how many patients have each condition, I recommend that you not use a single field to collect this data. It will be better to set up a related table linked by PatientID to your current table where each record records one such value. A portal to this related table with a drop down list or pop up menu of the values you want to put in your check box group is the simplest to set up, but it is possible to turn your portal into something that looks and functions like a standard check box set, but the values are recorded in individual related records so that a chart based on this related table can show you how many (or the percentages) individuals report each condition that you've listed in your value list.
Thanks Chamblee for your sample, is very useful.
I think single fields will be.
Thank you both