Example of a Covering Array with Factor Level Restrictions

The following example is patterned after an example described in Dalal and Mallows (1998). An originating phone (Near Phone) calls a receiving phone (Far Phone). Each phone call goes through an interface of type A or B. Five factors are of interest:

• Market: USA, UK, Canada, France, Mexico

• Near Phone: ISDN, Bus (Business), Coin, Res (Residential)

• Near Interface: A or B

• Far Phone: ISDN, Bus (Business), Coin, Res (Residential)

• Far Interface: A or B

You are interested in which combinations of pairs of these factors are likely to cause failures. However, certain combinations are not possible:

• An ISDN line on either phone (Near or Far) cannot use interface A.

• Business and Residential lines on the originating phone (Near) cannot use interface B.