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Usability


This graph was generated using the Usability Scorecard web-application. The Usability Scorecard takes any combination of raw usability metrics (time on task, satisfaction, completion rates and errors), standardizes them into z-scores, then summarizes them into a composite Single Usability Metric (SUM)

Premium Usability: Getting the Discount without Paying the Price
The Risks of Discounted Qualitative Studies:

Single Usability Metric (SUM)

SUM is a single usability metric that summarize the majority of variation in four common summative usability metrics. The theoretical foundations of the model are explained in the CHI paper. A more detailed practitioners guide was presented at UPA and a case study on using SUM to compare the usability of competing products was presented at HCII

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Statistics

Confidence Intervals

Confidence Intervals show the uncertainty of an estimate and can help Restore Confidence in Usability Results. Calculators are available for Completion Rate (Binomial) or Task Time Confidence Intervals.

Sample Size

The sample size will affect the amount of uncertainty in an estimate. Its calculation depends on the type data. Calculators are available for Task Completion, Time on Task and Discovering Problems in an Interface. In usability studies, the task context is important for sample sizes.

Ask a Statistics Question

What is the critical z score for a one tailed test with alpha = .01. Where can I find a Z score chart ? What is the connection between the confidence level and the confidence interval? More ...

For a refresher on some statistical concepts see the UsableStatistics section.

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Six Sigma
How Do You Calculate a Z-Score/ Sigma Level?
Making Sense of Usability Metrics: Usability and Six Sigma
Calculating a Sigma Level from Task Success
What's a Z-Score and Why Use it in Usability Testing?

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