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
Enter the area under the normal curve (a proportion between 0 & 1) and get the Z-critical value, one-sided or two-sided.
How Do You Calculate a Z-Score/ Sigma Level?
The basics of z-scores are discussed plus an example of raw usability data converted into z-scores including three of Nielsen's five usability attributes.
Making Sense of Usability Metrics: Usability and Six Sigma Presented at UPA 2005
This paper identifies the limitations of traditional usability metrics and presents a process to increase their meaning by adapting Six Sigma methods. We define how common usability metrics can be evaluated in terms of a standardized defective rate or quality level and explore the benefits of this data transformation. Use the Usability Scorcard or the excel-based SUM calculator to standardize your metrics.
Calculating a Sigma Level from Task Success
Often the most reported measures of usability is task success. How does task success translate into a quality sigma value that can be compared to other reported sigma values?
What's a Z-Score and Why Use it in Usability Testing?
This common statistical way of describing data can be used in usability testing to standardize disparate data types to allow easy comparison between products or versions and providing a universal way of assessing quality.
Why 6σ is Not Limited to Manufacturing Processes
One of the most common concerns about the six sigma methodology is that it cannot apply to something as byzantine as the interactions of humans with software. One of the major tenets of both Six Sigma and Human Factors is that the customer or user determine what's considered "quality."
What's the 1.5σ Shift and Does it Apply to Software Usability?
Conventional six sigma commonly adds a 1.5 sigma buffer to account for the shifting of a process over time. Does this make sense for software usability?
What is an Acceptable Level of Quality for Usability?
Is attaining Six Sigma a reasonable or even attainable goal for usability? A product's usability is the sum of several usability measures. Each Relative movement in your sigma value is good predictor of usability improvements.