It is possible to select one or multiple options in a checkbox field. In the export, every option becomes a variable, which looks like: variabelename#optionname

If the option has been selected, then the value of this field will be equal to 1. If the option has not been selected, then the value of this field will be equal to 0.

For example, a checkbox field has the variable name his_family. The field has the options Renal disease, Deafness, (Cardio)myopathy, Encephalopathy, Diabetes Mellitus, Hypertension/Cardiovascular disease, Thrombosis, and Malignancy. For this field two options are selected, e.g. Deafness and Diabetes Mellitus:

After exporting the checkbox data, a separate column will be generated for each option with the value "1" saved for each selected option (i.e., his_family#Deafness and his_family#Diabetes_Mellitus) and 0 for any option which was not selected:

It is not possible to have 1 variable in your export for a checkbox field which has multiple answer options.