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A Method for Estimating Bounds on System Reliability in the Absence of Times-to-Failure Data

A common method for obtaining confidence bounds on a system uses the variance of reliability of each component in the system along with the system reliability equation. This analytical method (discussed in the August 2009 issue of Reliability HotWire) requires that you have failure data for each component in the system. If times-to-failure data are not available for all components (e.g., the reliability information is obtained from a supplier who will share the distribution parameters, but not the actual failure data), some reliability engineers use a worst case/best case method based on the lower or upper confidence bounds for the parameters of the components. However, when data are available to compare the results, this approach provides estimates that are quite far from the analytical solution.


This article introduces a simulation method of obtaining approximate bounds on system reliability that does not require data for each component, but provides results that are closer to the analytical solution.


Read the Latest Reliability News

Excellent Presentation Awards at ARDC Europe

On behalf of the reliability, durability and maintainability community, we would like to thank all the presenters, sponsors and exhibitors at the 2017 ARDC Europe in Milan, Italy for creating such an engaging experience for new and returning attendees. Also, many congratulations to the award winners of this conference's most excellent presentations (as voted by the attendees).


  • 1st Place (Gold) - Marco Bonato of Valeo
    Reliability of Automotive Tier 2 Suppliers: Lesson Learned from In‐Service Early Failures
  • 2nd Place (Silver) - Freek van Beek of ASML
    What if You Can't Live With a Safety Factor: Statistics Combining Expert Knowledge with Measured Data
  • 3rd Place (Bronze) - Kim Albert Schmidt of DELTA
    New Possibilities for Simulation and Testing of Humidity Ingress in Real Products


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ReliaSoft Solutions at ESTECH Conference

HBM Prenscia exhibited at the ESTECH 2017 Conference in Louisville, Kentucky on May 8-11, 2017. Thank you to everyone who participated in this year's event and came to visit the HBM Prenscia booth. We enjoyed our discussions, and we look forward to future correspondence!


Reliability Test Design: Linking Fatigue and Reliability

Register to attend an upcoming reliability and durability webinar on May 22, 2017. This 45-minute webinar will introduce reliability to durability testing by showcasing test specifications, the use of reliability and confidence levels, determining the number of samples to be tested and setting the duration of the test. For more information and to register, visit:


Connect with ReliaSoft at AA&S Conference

HBM Prenscia will be exhibiting at the 2017 Aircraft Airworthiness & Sustainment (AA&S) Conference in Phoenix, AZ on May 22 – 25, 2017. Visit us at our booth to talk with our experts and to learn more about innovative concepts for improving reliability, availability, maintainability, safety and durability while reducing risk across a broad range of applications within the aerospace industry. If you're not able to attend the expo, you can learn more about ReliaSoft's aerospace solutions at

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