Quantifying the User Experience: Practical Statistics for User Research

Whenever you can establish that data is ratio, you can make reasonable deductions, such as “customers are twice as satisfied

You can cross-tab responses to the Net Promoter question with other important questions about future revenue and include confidence intervals.

The three factors that affect power are sample size, variability in the population, and the effect size.

If you have multiple metrics, one possibility proposed by Roy (2001) is to normalize each metric to a predefined range, say 0–1, and assign each a weight. Your OEC is the weighted sum of the normalized metrics.