Designing Effective Speech Interfaces

Cost-Benefit Calculations

We can calculate the costs and benefits of applying usability engineering to incorporate human factors into the design of a specific product. Let's demonstrate through an imagined scenario.

We have a telephony speech application that processes requests from customers. The average revenue per customer is $50. If we use human factors to improve the prompting of the system, we anticipate we will have two benefits: first, we will induce potential customers to become actual consumers of our product, and second, we will be able to process more customers in a day. Let's assume a rate of ten calls an hour. By improving prompting, we can raise that to 12 calls per hour. Based on a 16-hour day, we now handle 32 additional callers per day. If our sell rate on customers is 25 percent, we will have added eight customers per day for a total of $400 per day additional revenue.

If our system is selling seven days a week, then $400 per day is $146,000 a year, and $1,460,000 over a 10-year period. If the design improvement used $25,000 in design resources, then we will recoup our investment in about two months.

Let's take a different scenario—a command-and-control industrial application. There are 1000 users who use this application at several plants around the world. The users work 230 days per year at an average wage of $18 per hour, including benefits. Let's assume that by applying human factors to the speech system we are able to save each user a minimum of 60 seconds ...