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12.4  Custom software   349




                  extent and granularity of the instrumentation, you might consider exactly what you
                  need to capture. In some cases, individual mouse movements and key strokes might
                  be needed, while other studies might need only higher-level user actions, such as
                  selection of the “paste” operation. Careful attention to the relationship between
                  your experimental hypotheses—what do you hope to learn?—and the data col-
                  lected may help increase your chances of success. Another successful strategy in-
                  volves associating each recorded action with one or more categories, allowing ease
                  of processing and filtering by criteria appropriate to an analysis. This approach
                  might allow comparison of keyboard and mouse-movement records to higher-level
                  task indicators.


                  12.4.2   RESEARCH SOFTWARE
                  Another class of custom software tools for automatic data collection involves soft-
                  ware that is explicitly created for the sole purpose of running an experiment. These
                  tools generally present users with a series of tasks to be completed and record data
                  regarding task completion time, errors, and whatever other data may be neces-
                  sary. The Fitts' Law, Children, and Mouse Control sidebar discusses an example
                  of a custom software package developed for a study of how well young children
                  use computer mice. Researchers interested in studying how well young children
                  use a mouse built a tool that tracked task completion time as well as the trajec-
                  tory of mouse movements in tasks that involved moving between two targets. This
                  study found that younger children were much less accurate mouse users than adults
                  (Hourcade et al., 2004).


                   FITTS' LAW, CHILDREN, AND MOUSE CONTROL

                   Full-size computer keyboards, keypads on phone and small devices, mice,
                   trackballs, jog wheels, and joysticks are familiar controls for computers
                   and other electronic devices, but familiarity does not necessarily imply
                   understanding. How do we use these tools? How efficient are we? What sort
                   of mistakes do we make? What are the factors that determine task completion
                   time, accuracy, and error rate? Although researchers—in cognitive psychology
                   and more recently in HCI—have been asking these and similar questions for
                   more than 50 years, detailed study of the human use of these devices can still
                   lead us to valuable insights.
                      Target selection is an important task in this area. Given multiple targets
                   that a user might want to select—keys on a keyboard or buttons on a graphical
                   user interface—what determines how quickly and accurately a user can move
                   from one to another? Studies of target selection performance guide the size and
                   selection of graphical icons, placement of buttons on a cell-phone keypad, and
                   many other aspects of interface design.
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