Database Reference
In-Depth Information
4.10 EXERCISES
1. Consider tasks 6, 7, and 8 of Table 4.1 . Test the hypothesis that there is no
difference in the true pass/fail rates for the three tasks. The input and output in
Excel are in a ile named Chapter 4.Exercise 1. In SPSS, the input is in a ile
Chapter 4..Exercise 1.input and the output is in a ile named Chapter 4..Exercise
1.output.
A Word ile (ile name: Chapter 4.Exercise 1.discussion) is also provided, which
discusses the results.
2. Use the adjusted Wald method to ind a 95% conidence interval for the true
proportion who successfully complete the tasks, if we sample 20 people and
four successfully completed the task out of the 20. The answer and discussion
are in a Word ile named Chapter 4.Exercise 2.
REFERENCES
Agressi, A., Coull, B., 1998. Approximate is better than 'exact' for interval estimation of
binomial proportions. The American Statistician 52, p119-126.
Sauro, J., Lewis, J., 2005. Estimating completion rates from small samples using binomial
conidence intervals: comparisons and recommendations. In: Proceedings of the Human
Factors and Ergonomics Society Annual Meeting, Orlando, FL. Morgan Kaufmann. www.
measuringusability.com/papers/sauro-lewisHFES.pdf .
Lewis, J., Sauro, J., 2006. When 100% really isn't 100%: improving the accuracy of small-
sample estimates of completion rates. Journal of Usability Studies 1 (3), 136-150.
 
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