Did we meet or exceed our goal?
Abstract
This chapter covers methods for determining whether a design has met or exceeded a specific goal. The statistical test you use for completion rates depends on the sample size: A sample size is considered small unless you have more than 15 successes and 15 failures. For determining whether a certain percentage of users can complete a task for small sample sizes use the midprobability from the binomial distribution. For determining whether a certain percentage of users can complete a task for large sample sizes use the normal approximation to the binomial. You can always convert continuous rating scale data into discrete-binary data and test a percentage that agrees with a statement, but in so doing, ...
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