| Confidence Intervals |
| Confidence Interval Calculator for a Completion Rate If you've wanted to provide a confidence interval around a small sample completion rate but just didn't have time to do the math, this calculator does the work for you. Graph and Calculator for Confidence Intervals for Task Times Usable Statistics Restoring Confidence in Usability Results Margins of Error in Usability Tests The 20/20 Rule of Precision |
| Statistical Methods & Techniques |
| Z-Score to Percentile Calculator Look up the area under the normal curve (1 or two-sided areas) from a standard score (Z-score). Percentile to Z-Score Calculator How Do You Calculate a Z-Score/ Sigma Level? Calculating a Sigma Level from Task Success Usable Statistics What's a Z-Score and Why Use it in Usability Testing? Margins of Error in Usability Tests The 20/20 Rule of Precision |
| Sample Size |
| Sample Size Calculator for Discovering Problems in a User Interface Use this calculator to determine the number of users you'd need to test given the probability of detecting a problem. If the probability of detecting the problem is unknown, this calculator also allows you to estimate the problem occurrence (p) from sample data. Calculating Sample Size for Task Completion (Discrete-Binary Method) Calculating Sample Size for Task Times (Continuous Method) Deriving a Problem Discovery Sample Size Side-bar to The Risks of Discounted Qualitative Studies: Task Times in Formative Usability Tests Margins of Error in Usability Tests The 20/20 Rule of Precision |
| Six Sigma |
| Z-Score to Percentile Calculator Look up the area under the normal curve (1 or two-sided areas) from a standard score (Z-score). Percentile to Z-Score Calculator How Do You Calculate a Z-Score/ Sigma Level? Making Sense of Usability Metrics: Usability and Six Sigma Presented at UPA 2005 Calculating a Sigma Level from Task Success What's a Z-Score and Why Use it in Usability Testing? Why 6σ is Not Limited to Manufacturing Processes What's the 1.5σ Shift and Does it Apply to Software Usability? What is an Acceptable Level of Quality for Usability? |
