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Chapter 4 Evaluation of Text Entry Techn... > 4.5 SUMMARY AND FURTHER READING - Pg. 97

4.5 Summary and Further Reading 97 The equation for each condition is shown beside its curve in Fig. 4.13b. The equation is in the power form and is derived using a statistics application or a spread- sheet such as Microsoft Excel. The crossover phenomenon in Fig. 4.12 appears at the 10th session in Fig. 4.13. An extrapolation beyond the period of practice is also shown, although this obviously bears increasing inaccuracy the farther it extends beyond the test period. While the plots in Fig. 4.13b are instructive, often the most significant point is the first one--the measured performance during initial exposure to the technique. This point reflects the walk-up usability (a.k.a. immediate usability) of the technique. Researchers are often seeking to develop a text entry technique that improves on a current, established, but less-than-ideal technique. If there is a community of users familiar with the current technique, it is a tough sell to convince them to switch. Performance advantages of a new technique are often expected with minimal effort. In view of this researchers have developed evaluation methodologies designed specif- ically to capture the immediately usability of a technique, for example, by limiting and tightly controlling participants exposure to the technique. In one experiment, participants were given just 1 minute of exposure before performance measures were gathered (MacKenzie & Zhang, 1997). A second round of testing was done following an additional 5 minutes of exposure. Others have adopted similar evaluation meth-