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AC18: Predictive Evaluation

The purpose of this activity is to learn more about predicting usability using engineering models, specifically the keystroke-level model discussed in class. You will find a web browser useful for this activity, but not essential.

1. Drop-down vs. Textbox

Suppose we're designing a form for entering an address, and we're trying to decide between the two alternative interfaces for entering a US state shown below. The interface on the left is a drop-down menu with a list of states to choose from, and the interface on the right is a text field for entering the state's 2-letter abbreviation (e.g. MA for Massachusetts).

State: State:

Use the keystroke-level model to model the process of choosing Massachusetts using each of the following methods. Assume that the keyboard focus is already on the State field, and the user's hands are already on the device they need. Start by writing down the actions required; then assign K, P, H, M, and D labels to each action; and finally estimate the total time.

Method A: Using the mouse to pick Massachusetts from the drop-down menu. (Use the simplest form of the Pointing operator to estimate the times.)

Method B: Using the keyboard to pick Massachusetts from the drop-down menu. (There are several ways to do this; pick one.)

Method C: Using the keyboard to type MA into the text box.

Now imagine this interface in the context of an address form, in which it is usually preceded by a City field:

City: State:

Assuming the user has just finished typing the city name, extend your modeling to include the cost of getting to the State field.

Method A: Using the mouse for the whole method

Method B & C: Using the keyboard for the whole method.

Overall, which of the three methods is most efficient?

Which dimensions of usability are not being modeled by keystroke-level modeling, and how do the two interfaces compare on these dimensions?

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