Internally, a Yes/No field stores the values -1 for True, and 0 for False,
so if you sum them, you'll get negative values (-1 + -1 = -2). You could try
Linda's suggestion using IIf(), or you could use the Abs() function (Abs(-1)
= 1) or if you may be able to use Count() instead of Sum(). For example,
using the Products table from the Northwind sample database as an example,
this query returns -8 ...
SELECT Sum(Discontinued) AS SumOfDiscontinued
FROM Products
WHERE Discontinued = True
.... but this query returns 8 ...
SELECT Count(Discontinued) AS CountOfDiscontinued
FROM Products
WHERE Discontinued = True