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Cart Comparison Measures

When testing voice ordering systems, we use three measures to compare a submitted shopping cart to the expected cart.

  • Perfect - a submitted cart is said to be perfect if it has the same contents, in the same order, as the expected cart.
  • Complete - a submitted cart is said to be complete if it has the same contents, in any order.
  • Repair Cost - the number of edits required to make the submitted cart complete.

The first two measures, Perfect and Complete, are easy to compute and require no knowledge of the menu or point-of-sale (POS) user interface. The Perfect metric is useful when the customer can see the order, live, as it is being entered and expects it to match the flow of the conversation. In situations where there is no live feedback, the Complete metric is important in ensuring that the customer actually receives the correct items. Because of their all-or-none nature, these two measures are mainly useful for systems with extremely low error-rates.

In systems with even modest error rates, the Perfect and Complete measures may too blunt because a large number of nearly-complete orders will fail both measures. In this situation, the Repair Cost measure is needed to ascertain how close the cart comes to the ideal.

One challenge with the Repair Cost measure is that its implementation requires knowledge of the menu and assumptions about the user interface for correcting orders. Typically one can change an attribute (e.g. tall to grande) or a quantity (e.g. 1 to 2) or delete a product or option in a single operation. Changing the base product (e.g. latte to mocha) or base option (e.g. cinnamon syrup to vanilla syrup) is more costly because it involves deleting a fully configured product and then adding and configuring a new product. Understanding the cost of configuring a newly added product requires knowledge of default quantities and attributes.

As an example, adding 5 iced tall lattes would require four steps:

  • Adding a latte which defaults to 1 grande latte.
  • Changing the size to tall.
  • Changing the form to iced.
  • Changing the quantity to 5.

Adding one latte in the default size would require only one step:

  • Adding a latte which defaults to 1 grande latte.

In the following we consider nine scenarios that illustrate the Perfect, Complete, and Repair Cost measures. In each of the nine examples, below, we expect the following cart:

1 tall latte (601)
  1 no foam (5200)
  2 vanilla syrup (2502)
1 apple bran muffin (10000)
  1 warmed (200)

Here's a summary of the measures for each of the nine cases:

Scenario Perfect Complete Repair
Carts are identical ✔ ✔ 0
Products out of order ❌ ✔ 0
Product SKU wrong because generic product is wrong ❌ ❌ varies
Product SKU wrong because one or more attributes are wrong ❌ ❌ varies
Product quantity wrong ❌ ❌ 1
Options out of order ❌ ✔ 0
Option SKU wrong because generic option is wrong ❌ ❌ varies
Option SKU wrong because one or more attributes are wrong ❌ ❌ varies
Option quantity wrong ❌ ❌ 1

Carts are identical

Perfect Complete Repair
✔ ✔ 0

The expected cart is identical to the submitted cart:

1 tall latte (601)
  1 no foam (5200)
  2 vanilla syrup (2502)
1 apple bran muffin (10000)
  1 warmed (200)

Since the cart is perfect and complete, no repairs are required.

Products out of order

Perfect Complete Repair
❌ ✔ 0

In this case, the apple bran muffin appears before the tall latte.

1 apple bran muffin (10000)
  1 warmed (200)   
1 tall latte (601)
  1 no foam (5200)
  2 vanilla syrup (2502)

Since the cart is complete, no repairs are required.

Product SKU wrong because generic product is wrong

Perfect Complete Repair
❌ ❌ 7

In this case, a tall mocha appears where we expect a tall latte.

1 tall mocha (801)
  1 no foam (5200)
  2 vanilla syrup (2502)
1 apple bran muffin (10000)
  1 warmed (200)

Repairing the cart involves seven edits:

  • Remove the tall mocha along with its options.
  • Add a latte, which is, by default, a grande.
  • Change its size to tall.
  • Add the foam option.
  • Change its attribute to no.
  • Add the vanilla syrup option
  • Change its quantity to 2.

One could image an alternatve point-of-sale (POS) UI that would allow one to replace the mocha with a latte while leaving its attributes, options, and quantities intact. In this case, the repair cost would be 1.

Product SKU wrong because one or more attributes are wrong

Perfect Complete Repair
❌ ❌ 2

In this case, iced and venti appear where tall was expected.

1 iced venti latte (605)
  1 no foam (5200)
  2 vanilla syrup (2502)
1 apple bran muffin (10000)
  1 warmed (200)

Repairing the cart involves two edits:

  • Changing the venti attribute to tall.
  • Removing the iced attribute.

Product quantity wrong

Perfect Complete Repair
❌ ❌ 1

This cart contains 5 drinks where we expect 1.

5 tall latte (601)
  1 no foam (5200)
  2 vanilla syrup (2502)
1 apple bran muffin (10000)
  1 warmed (200)

Repairing the case involves one edit:

  • Change quantity to 5.

Options out of order

Perfect Complete Repair
❌ ✔ 0

In this cart, vanilla syrup appears before no foam.

1 tall latte (601)
  2 vanilla syrup (2502)
  1 no foam (5200)
1 apple bran muffin (10000)
  1 warmed (200)

Since the cart is complete, no repairs are required.

Option SKU wrong because generic option is wrong

Perfect Complete Repair
❌ ❌ 3

In this cart, cinnamon syrup appears where we expect vanilla syrup.

1 tall latte (601)
  1 no foam (5200)
  2 cinnamon syrup (1902)
1 apple bran muffin (10000)
  1 warmed (200)

Repairing the cart involves three edits:

  • Remove the cinnamon syrup.
  • Add vanilla syrup.
  • Change its quantity to 2.

Again, one could imagine an alternative POS UI that would allow one to swap vanilla syrup for cinnamon syrup, while leaving the quatity intact. In this case, the repair cost would be 1.

Option SKU wrong because one or more attributes are wrong

Perfect Complete Repair
❌ ❌ 1

In this cart, extra foam appears where we expect no foam.

1 tall latte (601)
  1 extra foam (5203)
  2 vanilla syrup (2502)
1 apple bran muffin (10000)
  1 warmed (200)

Repairing the cart involves one edit:

  • Change extra to no.

Option quantity wrong

Perfect Complete Repair
❌ ❌ 1

This cart has 5 vanilla syrup where we expect 2:

1 tall latte (601)
  1 no foam (5200)
  5 vanilla syrup (2502)
1 apple bran muffin (10000)
  1 warmed (200)

Repairing the cart involves one edit:

  • Change syrup quantity from 5 to 2.