Simple Question About Checkboxes

I would like to know how to properly use checkboxes in a form as criteria in a query. Specifically how to get an iif statement to evaluate whether or not a check box in a form is checked

Take a very simple example of a database containing a employees of two types. Two tables exist; an employee table, and an employee type table.

I then want to make an easy to use interface for getting a query of employee information for one or both employee types.

I figured that the best way to do this would be to create a form with a checkbox for each type and then create a query that uses an iif statement like this:

IIf([Forms]![employee_type_query_frm]![Check_type1]=YES,"1",Null) Or IIf([Forms]![employee_type_query_frm]![Check_type2]=YES,"2",Null)

Where one is the number associated with employee type 1 and 2 is the number associated with employee type 2.

Then I just build a simple macro in the form to run the query. This way someone who doesn't know how to work in the query interface can open the form, click the checkboxes for the type of employees that they need information on and run the query by pressing a command button.

The problem is that I don't know/can't find the proper syntax for getting the iff statement to evaluate if the checkboxes in the form are checked or not.

If anyone could give me some advice it would be very much appreciated.

PS: here is the full SQL of the example Query
SELECT employee_tbl.[employee#], employee_tbl.employee_name, employee_tbl.employee_type
FROM employee_type INNER JOIN employee_tbl ON employee_type.employee_type = employee_tbl.employee_type
WHERE (((employee_tbl.employee_type)=IIf([Forms]![employee_type_query_frm]![Check_type1]=1,"1",Null) Or (employee_tbl.employee_type)=IIf([Forms]![employee_type_query_frm]![Check_type2]=1,"2",Null)));