Articles by Bernard Rummel

Trained in experimental psychology, Mr. Rummel has been working in the Usability and UI Design field for over 20 years. After nine years at the German Naval Medical Institute, he joined SAP in 2000, where he is currently responsible for online usability testing methodology and participating in the national standardization body DIN.

Invited Essay: About Time: A Practitioner’s Guide to Task Completion Time Analysis

Prologue In early 2012, I was in charge of defining SAP’s quantitative usability testing methodology. In search for a sound and solid efficiency KPI, I pondered the statistical properties of task completion times. Several papers (e.g., Sauro & Lewis, 2010) stated those times were not normally distributed, but what was their distribution? The distribution tests […] [Read More]

Predicting Post-Task User Satisfaction With Weibull Analysis of Task Completion Times

Abstract Task completion times have been shown to follow Weibull distributions, with parameters reflecting different aspects of the task solution process (Rummel, 2017). The offset time matches UI operation time, including system response time, on the shortest path taken by users (“click time”). The characteristic time describes the solution rate in the stochastic process of […] [Read More]

Beyond Average: Weibull Analysis of Task Completion Times

Abstract Weibull analysis is an established method in technical reliability analysis for describing and analyzing the lifetime of technical parts. This paper describes the approach and demonstrates its application on task completion times from small-sample usability tests. Fitting a Weibull distribution model to observed data lets the analyst estimate task completion rates for any given […] [Read More]

Probability Plotting: A Tool for Analyzing Task Completion Times

Abstract Task completion time is a valuable metric for assessing or comparing the usability of a product. In online, unmoderated usability tests and other automated user behavior tracking methods, the large amount of time data that such tests yield must be carefully examined to exclude invalid data before further analysis can be meaningful. Other methodological […] [Read More]